diff --git a/core/builtins/native/kotlin/Annotation.kt b/core/builtins/native/kotlin/Annotation.kt
index 1f6db4aaeed..5557fddb15f 100644
--- a/core/builtins/native/kotlin/Annotation.kt
+++ b/core/builtins/native/kotlin/Annotation.kt
@@ -17,8 +17,8 @@
 package kotlin
 
 /**
- * Base trait implicitly implemented by all annotation interfaces.
+ * Base interface implicitly implemented by all annotation interfaces.
  * See [Kotlin language documentation](http://kotlinlang.org/docs/reference/annotations.html) for more information
  * on annotations.
  */
-public trait Annotation
+public interface Annotation
diff --git a/core/builtins/native/kotlin/CharSequence.kt b/core/builtins/native/kotlin/CharSequence.kt
index a251e3b7064..e3ebc00c84f 100644
--- a/core/builtins/native/kotlin/CharSequence.kt
+++ b/core/builtins/native/kotlin/CharSequence.kt
@@ -19,7 +19,7 @@ package kotlin
 /**
  * Represents a readable sequence of [Char] values.
  */
-public trait CharSequence {
+public interface CharSequence {
     /**
      * Returns the length of this character sequence.
      */
diff --git a/core/builtins/native/kotlin/Cloneable.kt b/core/builtins/native/kotlin/Cloneable.kt
index 42d1837f548..7588573eae8 100644
--- a/core/builtins/native/kotlin/Cloneable.kt
+++ b/core/builtins/native/kotlin/Cloneable.kt
@@ -17,9 +17,9 @@
 package kotlin
 
 /**
- * Classes that inherit from this trait support creating field-by-field copies of their instances.
+ * Classes that inherit from this interface support creating field-by-field copies of their instances.
  */
-public trait Cloneable {
+public interface Cloneable {
     /**
      * Creates and returns a field-by-field copy of this object.
      */
diff --git a/core/builtins/native/kotlin/Collections.kt b/core/builtins/native/kotlin/Collections.kt
index d8bf8d4bd19..884cb0a2ad8 100644
--- a/core/builtins/native/kotlin/Collections.kt
+++ b/core/builtins/native/kotlin/Collections.kt
@@ -17,11 +17,11 @@
 package kotlin
 
 /**
- * Classes that inherit from this trait can be represented as a sequence of elements that can
+ * Classes that inherit from this interface can be represented as a sequence of elements that can
  * be iterated over.
  * @param T the type of element being iterated over.
  */
-public trait Iterable<out T> {
+public interface Iterable<out T> {
     /**
      * Returns an iterator over the elements of this object.
      */
@@ -29,10 +29,10 @@ public trait Iterable<out T> {
 }
 
 /**
- * Classes that inherit from this trait can be represented as a sequence of elements that can
+ * Classes that inherit from this interface can be represented as a sequence of elements that can
  * be iterated over and that supports removing elements during iteration.
  */
-public trait MutableIterable<out T> : Iterable<T> {
+public interface MutableIterable<out T> : Iterable<T> {
     /**
      * Returns an iterator over the elementrs of this sequence that supports removing elements during iteration.
      */
@@ -40,11 +40,11 @@ public trait MutableIterable<out T> : Iterable<T> {
 }
 
 /**
- * A generic collection of elements. Methods in this trait support only read-only access to the collection;
- * read/write access is supported through the [MutableCollection] trait.
+ * A generic collection of elements. Methods in this interface support only read-only access to the collection;
+ * read/write access is supported through the [MutableCollection] interface.
  * @param E the type of elements contained in the collection.
  */
-public trait Collection<out E> : Iterable<E> {
+public interface Collection<out E> : Iterable<E> {
     // Query Operations
     /**
      * Returns the size of the collection.
@@ -72,7 +72,7 @@ public trait Collection<out E> : Iterable<E> {
 /**
  * A generic collection of elements that supports adding and removing elements.
  */
-public trait MutableCollection<E> : Collection<E>, MutableIterable<E> {
+public interface MutableCollection<E> : Collection<E>, MutableIterable<E> {
     // Query Operations
     override fun iterator(): MutableIterator<E>
 
@@ -121,11 +121,11 @@ public trait MutableCollection<E> : Collection<E>, MutableIterable<E> {
 }
 
 /**
- * A generic ordered collection of elements. Methods in this trait support only read-only access to the list;
- * read/write access is supported through the [MutableList] trait.
+ * A generic ordered collection of elements. Methods in this interface support only read-only access to the list;
+ * read/write access is supported through the [MutableList] interface.
  * @param E the type of elements contained in the list.
  */
-public trait List<out E> : Collection<E> {
+public interface List<out E> : Collection<E> {
     // Query Operations
     override fun size(): Int
     override fun isEmpty(): Boolean
@@ -177,7 +177,7 @@ public trait List<out E> : Collection<E> {
  * A generic ordered collection of elements that supports adding and removing elements.
  * @param E the type of elements contained in the list.
  */
-public trait MutableList<E> : List<E>, MutableCollection<E> {
+public interface MutableList<E> : List<E>, MutableCollection<E> {
     // Modification Operations
     override fun add(e: E): Boolean
     override fun remove(o: Any?): Boolean
@@ -225,11 +225,11 @@ public trait MutableList<E> : List<E>, MutableCollection<E> {
 
 /**
  * A generic unordered collection of elements that does not support duplicate elements.
- * Methods in this trait support only read-only access to the set;
- * read/write access is supported through the [MutableSet] trait.
+ * Methods in this interface support only read-only access to the set;
+ * read/write access is supported through the [MutableSet] interface.
  * @param E the type of elements contained in the set.
  */
-public trait Set<out E> : Collection<E> {
+public interface Set<out E> : Collection<E> {
     // Query Operations
     override fun size(): Int
     override fun isEmpty(): Boolean
@@ -245,7 +245,7 @@ public trait Set<out E> : Collection<E> {
  * adding and removing elements.
  * @param E the type of elements contained in the set.
  */
-public trait MutableSet<E> : Set<E>, MutableCollection<E> {
+public interface MutableSet<E> : Set<E>, MutableCollection<E> {
     // Query Operations
     override fun iterator(): MutableIterator<E>
 
@@ -263,12 +263,12 @@ public trait MutableSet<E> : Set<E>, MutableCollection<E> {
 /**
  * A collection that holds pairs of objects (keys and values) and supports efficiently retrieving
  * the value corresponding to each key. Map keys are unique; the map holds only one value for each key.
- * Methods in this trait support only read-only access to the map; read-write access is supported through
- * the [MutableMap] trait.
+ * Methods in this interface support only read-only access to the map; read-write access is supported through
+ * the [MutableMap] interface.
  * @param K the type of map keys.
  * @param V the type of map values.
  */
-public trait Map<K, out V> {
+public interface Map<K, out V> {
     // Query Operations
     /**
      * Returns the number of key/value pairs in the map.
@@ -314,7 +314,7 @@ public trait Map<K, out V> {
     /**
      * Represents a key/value pair held by a [Map].
      */
-    public trait Entry<out K, out V> {
+    public interface Entry<out K, out V> {
         /**
          * Returns the key of this key/value pair.
          */
@@ -333,7 +333,7 @@ public trait Map<K, out V> {
  * @param K the type of map keys.
  * @param V the type of map values.
  */
-public trait MutableMap<K, V> : Map<K, V> {
+public interface MutableMap<K, V> : Map<K, V> {
     // Modification Operations
     /**
      * Associates the specified [value] with the specified [key] in the map.
@@ -368,7 +368,7 @@ public trait MutableMap<K, V> : Map<K, V> {
     /**
      * Represents a key/value pair held by a [MutableMap].
      */
-    public trait MutableEntry<K,V>: Map.Entry<K, V> {
+    public interface MutableEntry<K,V>: Map.Entry<K, V> {
         /**
          * Changes the value associated with the key of this entry.
          *
diff --git a/core/builtins/native/kotlin/Comparable.kt b/core/builtins/native/kotlin/Comparable.kt
index 19873815c9a..0fffb68bc14 100644
--- a/core/builtins/native/kotlin/Comparable.kt
+++ b/core/builtins/native/kotlin/Comparable.kt
@@ -17,9 +17,9 @@
 package kotlin
 
 /**
- * Classes which inherit from this trait have a defined total ordering between their instances.
+ * Classes which inherit from this interface have a defined total ordering between their instances.
  */
-public trait Comparable<in T> {
+public interface Comparable<in T> {
     /**
      * Compares this object with the specified object for order. Returns zero if this object is equal
      * to the specified [other] object, a negative number if it's less than [other], or a positive number
diff --git a/core/builtins/native/kotlin/Iterator.kt b/core/builtins/native/kotlin/Iterator.kt
index c85b955f561..8f6d2f0662c 100644
--- a/core/builtins/native/kotlin/Iterator.kt
+++ b/core/builtins/native/kotlin/Iterator.kt
@@ -20,7 +20,7 @@ package kotlin
  * An iterator over a collection or another entity that can be represented as a sequence of elements.
  * Allows to sequentially access the elements.
  */
-public trait Iterator<out T> {
+public interface Iterator<out T> {
     /**
      * Returns the next element in the iteration.
      */
@@ -36,7 +36,7 @@ public trait Iterator<out T> {
  * An iterator over a mutable collection. Provides the ability to remove elements while iterating.
  * @see MutableCollection.iterator
  */
-public trait MutableIterator<out T> : Iterator<T> {
+public interface MutableIterator<out T> : Iterator<T> {
     /**
      * Removes from the underlying collection the last element returned by this iterator.
      */
@@ -47,7 +47,7 @@ public trait MutableIterator<out T> : Iterator<T> {
  * An iterator over a collection that supports indexed access.
  * @see List.listIterator
  */
-public trait ListIterator<out T> : Iterator<T> {
+public interface ListIterator<out T> : Iterator<T> {
     // Query Operations
     override fun next(): T
     override fun hasNext(): Boolean
@@ -77,7 +77,7 @@ public trait ListIterator<out T> : Iterator<T> {
  * An iterator over a mutable collection that supports indexed access. Provides the ability
  * to add, modify and remove elements while iterating.
  */
-public trait MutableListIterator<T> : ListIterator<T>, MutableIterator<T> {
+public interface MutableListIterator<T> : ListIterator<T>, MutableIterator<T> {
     // Query Operations
     override fun next(): T
     override fun hasNext(): Boolean
diff --git a/core/builtins/src/kotlin/ExtensionFunctions.kt b/core/builtins/src/kotlin/ExtensionFunctions.kt
index 330650d6eed..1b4f7edb90e 100644
--- a/core/builtins/src/kotlin/ExtensionFunctions.kt
+++ b/core/builtins/src/kotlin/ExtensionFunctions.kt
@@ -19,117 +19,117 @@
 package kotlin
 
 /** An extension function that takes 0 arguments. */
-public trait ExtensionFunction0<in T, out R> {
+public interface ExtensionFunction0<in T, out R> {
     /** Invokes the function. */
     public fun T.invoke(): R
 }
 /** An extension function that takes 1 argument. */
-public trait ExtensionFunction1<in T, in P1, out R> {
+public interface ExtensionFunction1<in T, in P1, out R> {
     /** Invokes the function with the specified argument. */
     public fun T.invoke(p1: P1): R
 }
 /** An extension function that takes 2 arguments. */
-public trait ExtensionFunction2<in T, in P1, in P2, out R> {
+public interface ExtensionFunction2<in T, in P1, in P2, out R> {
     /** Invokes the function with the specified arguments. */
     public fun T.invoke(p1: P1, p2: P2): R
 }
 /** An extension function that takes 3 arguments. */
-public trait ExtensionFunction3<in T, in P1, in P2, in P3, out R> {
+public interface ExtensionFunction3<in T, in P1, in P2, in P3, out R> {
     /** Invokes the function with the specified arguments. */
     public fun T.invoke(p1: P1, p2: P2, p3: P3): R
 }
 /** An extension function that takes 4 arguments. */
-public trait ExtensionFunction4<in T, in P1, in P2, in P3, in P4, out R> {
+public interface ExtensionFunction4<in T, in P1, in P2, in P3, in P4, out R> {
     /** Invokes the function with the specified arguments. */
     public fun T.invoke(p1: P1, p2: P2, p3: P3, p4: P4): R
 }
 /** An extension function that takes 5 arguments. */
-public trait ExtensionFunction5<in T, in P1, in P2, in P3, in P4, in P5, out R> {
+public interface ExtensionFunction5<in T, in P1, in P2, in P3, in P4, in P5, out R> {
     /** Invokes the function with the specified arguments. */
     public fun T.invoke(p1: P1, p2: P2, p3: P3, p4: P4, p5: P5): R
 }
 /** An extension function that takes 6 arguments. */
-public trait ExtensionFunction6<in T, in P1, in P2, in P3, in P4, in P5, in P6, out R> {
+public interface ExtensionFunction6<in T, in P1, in P2, in P3, in P4, in P5, in P6, out R> {
     /** Invokes the function with the specified arguments. */
     public fun T.invoke(p1: P1, p2: P2, p3: P3, p4: P4, p5: P5, p6: P6): R
 }
 /** An extension function that takes 7 arguments. */
-public trait ExtensionFunction7<in T, in P1, in P2, in P3, in P4, in P5, in P6, in P7, out R> {
+public interface ExtensionFunction7<in T, in P1, in P2, in P3, in P4, in P5, in P6, in P7, out R> {
     /** Invokes the function with the specified arguments. */
     public fun T.invoke(p1: P1, p2: P2, p3: P3, p4: P4, p5: P5, p6: P6, p7: P7): R
 }
 /** An extension function that takes 8 arguments. */
-public trait ExtensionFunction8<in T, in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, out R> {
+public interface ExtensionFunction8<in T, in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, out R> {
     /** Invokes the function with the specified arguments. */
     public fun T.invoke(p1: P1, p2: P2, p3: P3, p4: P4, p5: P5, p6: P6, p7: P7, p8: P8): R
 }
 /** An extension function that takes 9 arguments. */
-public trait ExtensionFunction9<in T, in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, out R> {
+public interface ExtensionFunction9<in T, in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, out R> {
     /** Invokes the function with the specified arguments. */
     public fun T.invoke(p1: P1, p2: P2, p3: P3, p4: P4, p5: P5, p6: P6, p7: P7, p8: P8, p9: P9): R
 }
 /** An extension function that takes 10 arguments. */
-public trait ExtensionFunction10<in T, in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, in P10, out R> {
+public interface ExtensionFunction10<in T, in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, in P10, out R> {
     /** Invokes the function with the specified arguments. */
     public fun T.invoke(p1: P1, p2: P2, p3: P3, p4: P4, p5: P5, p6: P6, p7: P7, p8: P8, p9: P9, p10: P10): R
 }
 /** An extension function that takes 11 arguments. */
-public trait ExtensionFunction11<in T, in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, in P10, in P11, out R> {
+public interface ExtensionFunction11<in T, in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, in P10, in P11, out R> {
     /** Invokes the function with the specified arguments. */
     public fun T.invoke(p1: P1, p2: P2, p3: P3, p4: P4, p5: P5, p6: P6, p7: P7, p8: P8, p9: P9, p10: P10, p11: P11): R
 }
 /** An extension function that takes 12 arguments. */
-public trait ExtensionFunction12<in T, in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, in P10, in P11, in P12, out R> {
+public interface ExtensionFunction12<in T, in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, in P10, in P11, in P12, out R> {
     /** Invokes the function with the specified arguments. */
     public fun T.invoke(p1: P1, p2: P2, p3: P3, p4: P4, p5: P5, p6: P6, p7: P7, p8: P8, p9: P9, p10: P10, p11: P11, p12: P12): R
 }
 /** An extension function that takes 13 arguments. */
-public trait ExtensionFunction13<in T, in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, in P10, in P11, in P12, in P13, out R> {
+public interface ExtensionFunction13<in T, in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, in P10, in P11, in P12, in P13, out R> {
     /** Invokes the function with the specified arguments. */
     public fun T.invoke(p1: P1, p2: P2, p3: P3, p4: P4, p5: P5, p6: P6, p7: P7, p8: P8, p9: P9, p10: P10, p11: P11, p12: P12, p13: P13): R
 }
 /** An extension function that takes 14 arguments. */
-public trait ExtensionFunction14<in T, in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, in P10, in P11, in P12, in P13, in P14, out R> {
+public interface ExtensionFunction14<in T, in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, in P10, in P11, in P12, in P13, in P14, out R> {
     /** Invokes the function with the specified arguments. */
     public fun T.invoke(p1: P1, p2: P2, p3: P3, p4: P4, p5: P5, p6: P6, p7: P7, p8: P8, p9: P9, p10: P10, p11: P11, p12: P12, p13: P13, p14: P14): R
 }
 /** An extension function that takes 15 arguments. */
-public trait ExtensionFunction15<in T, in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, in P10, in P11, in P12, in P13, in P14, in P15, out R> {
+public interface ExtensionFunction15<in T, in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, in P10, in P11, in P12, in P13, in P14, in P15, out R> {
     /** Invokes the function with the specified arguments. */
     public fun T.invoke(p1: P1, p2: P2, p3: P3, p4: P4, p5: P5, p6: P6, p7: P7, p8: P8, p9: P9, p10: P10, p11: P11, p12: P12, p13: P13, p14: P14, p15: P15): R
 }
 /** An extension function that takes 16 arguments. */
-public trait ExtensionFunction16<in T, in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, in P10, in P11, in P12, in P13, in P14, in P15, in P16, out R> {
+public interface ExtensionFunction16<in T, in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, in P10, in P11, in P12, in P13, in P14, in P15, in P16, out R> {
     /** Invokes the function with the specified arguments. */
     public fun T.invoke(p1: P1, p2: P2, p3: P3, p4: P4, p5: P5, p6: P6, p7: P7, p8: P8, p9: P9, p10: P10, p11: P11, p12: P12, p13: P13, p14: P14, p15: P15, p16: P16): R
 }
 /** An extension function that takes 17 arguments. */
-public trait ExtensionFunction17<in T, in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, in P10, in P11, in P12, in P13, in P14, in P15, in P16, in P17, out R> {
+public interface ExtensionFunction17<in T, in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, in P10, in P11, in P12, in P13, in P14, in P15, in P16, in P17, out R> {
     /** Invokes the function with the specified arguments. */
     public fun T.invoke(p1: P1, p2: P2, p3: P3, p4: P4, p5: P5, p6: P6, p7: P7, p8: P8, p9: P9, p10: P10, p11: P11, p12: P12, p13: P13, p14: P14, p15: P15, p16: P16, p17: P17): R
 }
 /** An extension function that takes 18 arguments. */
-public trait ExtensionFunction18<in T, in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, in P10, in P11, in P12, in P13, in P14, in P15, in P16, in P17, in P18, out R> {
+public interface ExtensionFunction18<in T, in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, in P10, in P11, in P12, in P13, in P14, in P15, in P16, in P17, in P18, out R> {
     /** Invokes the function with the specified arguments. */
     public fun T.invoke(p1: P1, p2: P2, p3: P3, p4: P4, p5: P5, p6: P6, p7: P7, p8: P8, p9: P9, p10: P10, p11: P11, p12: P12, p13: P13, p14: P14, p15: P15, p16: P16, p17: P17, p18: P18): R
 }
 /** An extension function that takes 19 arguments. */
-public trait ExtensionFunction19<in T, in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, in P10, in P11, in P12, in P13, in P14, in P15, in P16, in P17, in P18, in P19, out R> {
+public interface ExtensionFunction19<in T, in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, in P10, in P11, in P12, in P13, in P14, in P15, in P16, in P17, in P18, in P19, out R> {
     /** Invokes the function with the specified arguments. */
     public fun T.invoke(p1: P1, p2: P2, p3: P3, p4: P4, p5: P5, p6: P6, p7: P7, p8: P8, p9: P9, p10: P10, p11: P11, p12: P12, p13: P13, p14: P14, p15: P15, p16: P16, p17: P17, p18: P18, p19: P19): R
 }
 /** An extension function that takes 20 arguments. */
-public trait ExtensionFunction20<in T, in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, in P10, in P11, in P12, in P13, in P14, in P15, in P16, in P17, in P18, in P19, in P20, out R> {
+public interface ExtensionFunction20<in T, in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, in P10, in P11, in P12, in P13, in P14, in P15, in P16, in P17, in P18, in P19, in P20, out R> {
     /** Invokes the function with the specified arguments. */
     public fun T.invoke(p1: P1, p2: P2, p3: P3, p4: P4, p5: P5, p6: P6, p7: P7, p8: P8, p9: P9, p10: P10, p11: P11, p12: P12, p13: P13, p14: P14, p15: P15, p16: P16, p17: P17, p18: P18, p19: P19, p20: P20): R
 }
 /** An extension function that takes 21 arguments. */
-public trait ExtensionFunction21<in T, in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, in P10, in P11, in P12, in P13, in P14, in P15, in P16, in P17, in P18, in P19, in P20, in P21, out R> {
+public interface ExtensionFunction21<in T, in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, in P10, in P11, in P12, in P13, in P14, in P15, in P16, in P17, in P18, in P19, in P20, in P21, out R> {
     /** Invokes the function with the specified arguments. */
     public fun T.invoke(p1: P1, p2: P2, p3: P3, p4: P4, p5: P5, p6: P6, p7: P7, p8: P8, p9: P9, p10: P10, p11: P11, p12: P12, p13: P13, p14: P14, p15: P15, p16: P16, p17: P17, p18: P18, p19: P19, p20: P20, p21: P21): R
 }
 /** An extension function that takes 22 arguments. */
-public trait ExtensionFunction22<in T, in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, in P10, in P11, in P12, in P13, in P14, in P15, in P16, in P17, in P18, in P19, in P20, in P21, in P22, out R> {
+public interface ExtensionFunction22<in T, in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, in P10, in P11, in P12, in P13, in P14, in P15, in P16, in P17, in P18, in P19, in P20, in P21, in P22, out R> {
     /** Invokes the function with the specified arguments. */
     public fun T.invoke(p1: P1, p2: P2, p3: P3, p4: P4, p5: P5, p6: P6, p7: P7, p8: P8, p9: P9, p10: P10, p11: P11, p12: P12, p13: P13, p14: P14, p15: P15, p16: P16, p17: P17, p18: P18, p19: P19, p20: P20, p21: P21, p22: P22): R
 }
diff --git a/core/builtins/src/kotlin/FloatingPointConstants.kt b/core/builtins/src/kotlin/FloatingPointConstants.kt
index dfe93baed24..c9990d96486 100644
--- a/core/builtins/src/kotlin/FloatingPointConstants.kt
+++ b/core/builtins/src/kotlin/FloatingPointConstants.kt
@@ -19,7 +19,7 @@ package kotlin
 /**
  * Holder for special values of floating point types.
  */
-public trait FloatingPointConstants<T> {
+public interface FloatingPointConstants<T> {
     /**
      * A constant holding the positive infinity value.
      */
diff --git a/core/builtins/src/kotlin/Functions.kt b/core/builtins/src/kotlin/Functions.kt
index 18a16c56e1c..81ac8c558bc 100644
--- a/core/builtins/src/kotlin/Functions.kt
+++ b/core/builtins/src/kotlin/Functions.kt
@@ -19,117 +19,117 @@
 package kotlin
 
 /** A function that takes 0 arguments. */
-public trait Function0<out R> {
+public interface Function0<out R> {
     /** Invokes the function. */
     public fun invoke(): R
 }
 /** A function that takes 1 argument. */
-public trait Function1<in P1, out R> {
+public interface Function1<in P1, out R> {
     /** Invokes the function with the specified argument. */
     public fun invoke(p1: P1): R
 }
 /** A function that takes 2 arguments. */
-public trait Function2<in P1, in P2, out R> {
+public interface Function2<in P1, in P2, out R> {
     /** Invokes the function with the specified arguments. */
     public fun invoke(p1: P1, p2: P2): R
 }
 /** A function that takes 3 arguments. */
-public trait Function3<in P1, in P2, in P3, out R> {
+public interface Function3<in P1, in P2, in P3, out R> {
     /** Invokes the function with the specified arguments. */
     public fun invoke(p1: P1, p2: P2, p3: P3): R
 }
 /** A function that takes 4 arguments. */
-public trait Function4<in P1, in P2, in P3, in P4, out R> {
+public interface Function4<in P1, in P2, in P3, in P4, out R> {
     /** Invokes the function with the specified arguments. */
     public fun invoke(p1: P1, p2: P2, p3: P3, p4: P4): R
 }
 /** A function that takes 5 arguments. */
-public trait Function5<in P1, in P2, in P3, in P4, in P5, out R> {
+public interface Function5<in P1, in P2, in P3, in P4, in P5, out R> {
     /** Invokes the function with the specified arguments. */
     public fun invoke(p1: P1, p2: P2, p3: P3, p4: P4, p5: P5): R
 }
 /** A function that takes 6 arguments. */
-public trait Function6<in P1, in P2, in P3, in P4, in P5, in P6, out R> {
+public interface Function6<in P1, in P2, in P3, in P4, in P5, in P6, out R> {
     /** Invokes the function with the specified arguments. */
     public fun invoke(p1: P1, p2: P2, p3: P3, p4: P4, p5: P5, p6: P6): R
 }
 /** A function that takes 7 arguments. */
-public trait Function7<in P1, in P2, in P3, in P4, in P5, in P6, in P7, out R> {
+public interface Function7<in P1, in P2, in P3, in P4, in P5, in P6, in P7, out R> {
     /** Invokes the function with the specified arguments. */
     public fun invoke(p1: P1, p2: P2, p3: P3, p4: P4, p5: P5, p6: P6, p7: P7): R
 }
 /** A function that takes 8 arguments. */
-public trait Function8<in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, out R> {
+public interface Function8<in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, out R> {
     /** Invokes the function with the specified arguments. */
     public fun invoke(p1: P1, p2: P2, p3: P3, p4: P4, p5: P5, p6: P6, p7: P7, p8: P8): R
 }
 /** A function that takes 9 arguments. */
-public trait Function9<in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, out R> {
+public interface Function9<in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, out R> {
     /** Invokes the function with the specified arguments. */
     public fun invoke(p1: P1, p2: P2, p3: P3, p4: P4, p5: P5, p6: P6, p7: P7, p8: P8, p9: P9): R
 }
 /** A function that takes 10 arguments. */
-public trait Function10<in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, in P10, out R> {
+public interface Function10<in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, in P10, out R> {
     /** Invokes the function with the specified arguments. */
     public fun invoke(p1: P1, p2: P2, p3: P3, p4: P4, p5: P5, p6: P6, p7: P7, p8: P8, p9: P9, p10: P10): R
 }
 /** A function that takes 11 arguments. */
-public trait Function11<in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, in P10, in P11, out R> {
+public interface Function11<in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, in P10, in P11, out R> {
     /** Invokes the function with the specified arguments. */
     public fun invoke(p1: P1, p2: P2, p3: P3, p4: P4, p5: P5, p6: P6, p7: P7, p8: P8, p9: P9, p10: P10, p11: P11): R
 }
 /** A function that takes 12 arguments. */
-public trait Function12<in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, in P10, in P11, in P12, out R> {
+public interface Function12<in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, in P10, in P11, in P12, out R> {
     /** Invokes the function with the specified arguments. */
     public fun invoke(p1: P1, p2: P2, p3: P3, p4: P4, p5: P5, p6: P6, p7: P7, p8: P8, p9: P9, p10: P10, p11: P11, p12: P12): R
 }
 /** A function that takes 13 arguments. */
-public trait Function13<in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, in P10, in P11, in P12, in P13, out R> {
+public interface Function13<in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, in P10, in P11, in P12, in P13, out R> {
     /** Invokes the function with the specified arguments. */
     public fun invoke(p1: P1, p2: P2, p3: P3, p4: P4, p5: P5, p6: P6, p7: P7, p8: P8, p9: P9, p10: P10, p11: P11, p12: P12, p13: P13): R
 }
 /** A function that takes 14 arguments. */
-public trait Function14<in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, in P10, in P11, in P12, in P13, in P14, out R> {
+public interface Function14<in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, in P10, in P11, in P12, in P13, in P14, out R> {
     /** Invokes the function with the specified arguments. */
     public fun invoke(p1: P1, p2: P2, p3: P3, p4: P4, p5: P5, p6: P6, p7: P7, p8: P8, p9: P9, p10: P10, p11: P11, p12: P12, p13: P13, p14: P14): R
 }
 /** A function that takes 15 arguments. */
-public trait Function15<in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, in P10, in P11, in P12, in P13, in P14, in P15, out R> {
+public interface Function15<in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, in P10, in P11, in P12, in P13, in P14, in P15, out R> {
     /** Invokes the function with the specified arguments. */
     public fun invoke(p1: P1, p2: P2, p3: P3, p4: P4, p5: P5, p6: P6, p7: P7, p8: P8, p9: P9, p10: P10, p11: P11, p12: P12, p13: P13, p14: P14, p15: P15): R
 }
 /** A function that takes 16 arguments. */
-public trait Function16<in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, in P10, in P11, in P12, in P13, in P14, in P15, in P16, out R> {
+public interface Function16<in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, in P10, in P11, in P12, in P13, in P14, in P15, in P16, out R> {
     /** Invokes the function with the specified arguments. */
     public fun invoke(p1: P1, p2: P2, p3: P3, p4: P4, p5: P5, p6: P6, p7: P7, p8: P8, p9: P9, p10: P10, p11: P11, p12: P12, p13: P13, p14: P14, p15: P15, p16: P16): R
 }
 /** A function that takes 17 arguments. */
-public trait Function17<in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, in P10, in P11, in P12, in P13, in P14, in P15, in P16, in P17, out R> {
+public interface Function17<in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, in P10, in P11, in P12, in P13, in P14, in P15, in P16, in P17, out R> {
     /** Invokes the function with the specified arguments. */
     public fun invoke(p1: P1, p2: P2, p3: P3, p4: P4, p5: P5, p6: P6, p7: P7, p8: P8, p9: P9, p10: P10, p11: P11, p12: P12, p13: P13, p14: P14, p15: P15, p16: P16, p17: P17): R
 }
 /** A function that takes 18 arguments. */
-public trait Function18<in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, in P10, in P11, in P12, in P13, in P14, in P15, in P16, in P17, in P18, out R> {
+public interface Function18<in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, in P10, in P11, in P12, in P13, in P14, in P15, in P16, in P17, in P18, out R> {
     /** Invokes the function with the specified arguments. */
     public fun invoke(p1: P1, p2: P2, p3: P3, p4: P4, p5: P5, p6: P6, p7: P7, p8: P8, p9: P9, p10: P10, p11: P11, p12: P12, p13: P13, p14: P14, p15: P15, p16: P16, p17: P17, p18: P18): R
 }
 /** A function that takes 19 arguments. */
-public trait Function19<in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, in P10, in P11, in P12, in P13, in P14, in P15, in P16, in P17, in P18, in P19, out R> {
+public interface Function19<in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, in P10, in P11, in P12, in P13, in P14, in P15, in P16, in P17, in P18, in P19, out R> {
     /** Invokes the function with the specified arguments. */
     public fun invoke(p1: P1, p2: P2, p3: P3, p4: P4, p5: P5, p6: P6, p7: P7, p8: P8, p9: P9, p10: P10, p11: P11, p12: P12, p13: P13, p14: P14, p15: P15, p16: P16, p17: P17, p18: P18, p19: P19): R
 }
 /** A function that takes 20 arguments. */
-public trait Function20<in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, in P10, in P11, in P12, in P13, in P14, in P15, in P16, in P17, in P18, in P19, in P20, out R> {
+public interface Function20<in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, in P10, in P11, in P12, in P13, in P14, in P15, in P16, in P17, in P18, in P19, in P20, out R> {
     /** Invokes the function with the specified arguments. */
     public fun invoke(p1: P1, p2: P2, p3: P3, p4: P4, p5: P5, p6: P6, p7: P7, p8: P8, p9: P9, p10: P10, p11: P11, p12: P12, p13: P13, p14: P14, p15: P15, p16: P16, p17: P17, p18: P18, p19: P19, p20: P20): R
 }
 /** A function that takes 21 arguments. */
-public trait Function21<in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, in P10, in P11, in P12, in P13, in P14, in P15, in P16, in P17, in P18, in P19, in P20, in P21, out R> {
+public interface Function21<in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, in P10, in P11, in P12, in P13, in P14, in P15, in P16, in P17, in P18, in P19, in P20, in P21, out R> {
     /** Invokes the function with the specified arguments. */
     public fun invoke(p1: P1, p2: P2, p3: P3, p4: P4, p5: P5, p6: P6, p7: P7, p8: P8, p9: P9, p10: P10, p11: P11, p12: P12, p13: P13, p14: P14, p15: P15, p16: P16, p17: P17, p18: P18, p19: P19, p20: P20, p21: P21): R
 }
 /** A function that takes 22 arguments. */
-public trait Function22<in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, in P10, in P11, in P12, in P13, in P14, in P15, in P16, in P17, in P18, in P19, in P20, in P21, in P22, out R> {
+public interface Function22<in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, in P10, in P11, in P12, in P13, in P14, in P15, in P16, in P17, in P18, in P19, in P20, in P21, in P22, out R> {
     /** Invokes the function with the specified arguments. */
     public fun invoke(p1: P1, p2: P2, p3: P3, p4: P4, p5: P5, p6: P6, p7: P7, p8: P8, p9: P9, p10: P10, p11: P11, p12: P12, p13: P13, p14: P14, p15: P15, p16: P16, p17: P17, p18: P18, p19: P19, p20: P20, p21: P21, p22: P22): R
 }
diff --git a/core/builtins/src/kotlin/Progression.kt b/core/builtins/src/kotlin/Progression.kt
index f912d4ddd48..9f245a43ac5 100644
--- a/core/builtins/src/kotlin/Progression.kt
+++ b/core/builtins/src/kotlin/Progression.kt
@@ -22,7 +22,7 @@ package kotlin
  * bytecode generation for it. Progressions with a step of -1 can be created through the
  * `downTo` method on classes representing primitive types.
  */
-public trait Progression<out N : Any> : Iterable<N> {
+public interface Progression<out N : Any> : Iterable<N> {
     /**
      * The start value of the progression.
      */
diff --git a/core/builtins/src/kotlin/PropertyMetadata.kt b/core/builtins/src/kotlin/PropertyMetadata.kt
index f7c473a280d..48b7c957de4 100644
--- a/core/builtins/src/kotlin/PropertyMetadata.kt
+++ b/core/builtins/src/kotlin/PropertyMetadata.kt
@@ -19,7 +19,7 @@ package kotlin
 /**
  * Represents a property in a Kotlin class.
  */
-public trait PropertyMetadata {
+public interface PropertyMetadata {
     /**
      * The name of the property.
      */
diff --git a/core/builtins/src/kotlin/Range.kt b/core/builtins/src/kotlin/Range.kt
index fad08d53c6d..aeff20cfaa3 100644
--- a/core/builtins/src/kotlin/Range.kt
+++ b/core/builtins/src/kotlin/Range.kt
@@ -20,7 +20,7 @@ package kotlin
  * Represents a range of values (for example, numbers or characters).
  * See the [Kotlin language documentation](http://kotlinlang.org/docs/reference/ranges.html) for more information.
  */
-public trait Range<T : Comparable<T>> {
+public interface Range<T : Comparable<T>> {
     /**
      * The minimum value in the range.
      */
diff --git a/core/builtins/src/kotlin/reflect/KCallable.kt b/core/builtins/src/kotlin/reflect/KCallable.kt
index 0f59c90242c..554d3d46fbb 100644
--- a/core/builtins/src/kotlin/reflect/KCallable.kt
+++ b/core/builtins/src/kotlin/reflect/KCallable.kt
@@ -21,7 +21,7 @@ package kotlin.reflect
  *
  * @param R return type of the callable.
  */
-public trait KCallable<out R> {
+public interface KCallable<out R> {
     /**
      * The name of this callable as it was declared in the source code.
      */
diff --git a/core/builtins/src/kotlin/reflect/KClass.kt b/core/builtins/src/kotlin/reflect/KClass.kt
index 552b7e68d8f..3a89c246fdb 100644
--- a/core/builtins/src/kotlin/reflect/KClass.kt
+++ b/core/builtins/src/kotlin/reflect/KClass.kt
@@ -24,7 +24,7 @@ package kotlin.reflect
  *
  * @param T the type of the class.
  */
-public trait KClass<T> {
+public interface KClass<T> {
     /**
      * The simple name of the class as it was declared in the source code,
      * or `null` if the class has no name (e.g. anonymous object literals).
diff --git a/core/builtins/src/kotlin/reflect/KExtensionFunctions.kt b/core/builtins/src/kotlin/reflect/KExtensionFunctions.kt
index 3ea1b55e5a4..615644126e1 100644
--- a/core/builtins/src/kotlin/reflect/KExtensionFunctions.kt
+++ b/core/builtins/src/kotlin/reflect/KExtensionFunctions.kt
@@ -19,48 +19,48 @@
 package kotlin.reflect
 
 /** An extension function with introspection capabilities that takes 0 arguments. */
-public trait KExtensionFunction0<in T, out R> : ExtensionFunction0<T, R>
+public interface KExtensionFunction0<in T, out R> : ExtensionFunction0<T, R>
 /** An extension function with introspection capabilities that takes 1 argument. */
-public trait KExtensionFunction1<in T, in P1, out R> : ExtensionFunction1<T, P1, R>
+public interface KExtensionFunction1<in T, in P1, out R> : ExtensionFunction1<T, P1, R>
 /** An extension function with introspection capabilities that takes 2 arguments. */
-public trait KExtensionFunction2<in T, in P1, in P2, out R> : ExtensionFunction2<T, P1, P2, R>
+public interface KExtensionFunction2<in T, in P1, in P2, out R> : ExtensionFunction2<T, P1, P2, R>
 /** An extension function with introspection capabilities that takes 3 arguments. */
-public trait KExtensionFunction3<in T, in P1, in P2, in P3, out R> : ExtensionFunction3<T, P1, P2, P3, R>
+public interface KExtensionFunction3<in T, in P1, in P2, in P3, out R> : ExtensionFunction3<T, P1, P2, P3, R>
 /** An extension function with introspection capabilities that takes 4 arguments. */
-public trait KExtensionFunction4<in T, in P1, in P2, in P3, in P4, out R> : ExtensionFunction4<T, P1, P2, P3, P4, R>
+public interface KExtensionFunction4<in T, in P1, in P2, in P3, in P4, out R> : ExtensionFunction4<T, P1, P2, P3, P4, R>
 /** An extension function with introspection capabilities that takes 5 arguments. */
-public trait KExtensionFunction5<in T, in P1, in P2, in P3, in P4, in P5, out R> : ExtensionFunction5<T, P1, P2, P3, P4, P5, R>
+public interface KExtensionFunction5<in T, in P1, in P2, in P3, in P4, in P5, out R> : ExtensionFunction5<T, P1, P2, P3, P4, P5, R>
 /** An extension function with introspection capabilities that takes 6 arguments. */
-public trait KExtensionFunction6<in T, in P1, in P2, in P3, in P4, in P5, in P6, out R> : ExtensionFunction6<T, P1, P2, P3, P4, P5, P6, R>
+public interface KExtensionFunction6<in T, in P1, in P2, in P3, in P4, in P5, in P6, out R> : ExtensionFunction6<T, P1, P2, P3, P4, P5, P6, R>
 /** An extension function with introspection capabilities that takes 7 arguments. */
-public trait KExtensionFunction7<in T, in P1, in P2, in P3, in P4, in P5, in P6, in P7, out R> : ExtensionFunction7<T, P1, P2, P3, P4, P5, P6, P7, R>
+public interface KExtensionFunction7<in T, in P1, in P2, in P3, in P4, in P5, in P6, in P7, out R> : ExtensionFunction7<T, P1, P2, P3, P4, P5, P6, P7, R>
 /** An extension function with introspection capabilities that takes 8 arguments. */
-public trait KExtensionFunction8<in T, in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, out R> : ExtensionFunction8<T, P1, P2, P3, P4, P5, P6, P7, P8, R>
+public interface KExtensionFunction8<in T, in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, out R> : ExtensionFunction8<T, P1, P2, P3, P4, P5, P6, P7, P8, R>
 /** An extension function with introspection capabilities that takes 9 arguments. */
-public trait KExtensionFunction9<in T, in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, out R> : ExtensionFunction9<T, P1, P2, P3, P4, P5, P6, P7, P8, P9, R>
+public interface KExtensionFunction9<in T, in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, out R> : ExtensionFunction9<T, P1, P2, P3, P4, P5, P6, P7, P8, P9, R>
 /** An extension function with introspection capabilities that takes 10 arguments. */
-public trait KExtensionFunction10<in T, in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, in P10, out R> : ExtensionFunction10<T, P1, P2, P3, P4, P5, P6, P7, P8, P9, P10, R>
+public interface KExtensionFunction10<in T, in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, in P10, out R> : ExtensionFunction10<T, P1, P2, P3, P4, P5, P6, P7, P8, P9, P10, R>
 /** An extension function with introspection capabilities that takes 11 arguments. */
-public trait KExtensionFunction11<in T, in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, in P10, in P11, out R> : ExtensionFunction11<T, P1, P2, P3, P4, P5, P6, P7, P8, P9, P10, P11, R>
+public interface KExtensionFunction11<in T, in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, in P10, in P11, out R> : ExtensionFunction11<T, P1, P2, P3, P4, P5, P6, P7, P8, P9, P10, P11, R>
 /** An extension function with introspection capabilities that takes 12 arguments. */
-public trait KExtensionFunction12<in T, in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, in P10, in P11, in P12, out R> : ExtensionFunction12<T, P1, P2, P3, P4, P5, P6, P7, P8, P9, P10, P11, P12, R>
+public interface KExtensionFunction12<in T, in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, in P10, in P11, in P12, out R> : ExtensionFunction12<T, P1, P2, P3, P4, P5, P6, P7, P8, P9, P10, P11, P12, R>
 /** An extension function with introspection capabilities that takes 13 arguments. */
-public trait KExtensionFunction13<in T, in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, in P10, in P11, in P12, in P13, out R> : ExtensionFunction13<T, P1, P2, P3, P4, P5, P6, P7, P8, P9, P10, P11, P12, P13, R>
+public interface KExtensionFunction13<in T, in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, in P10, in P11, in P12, in P13, out R> : ExtensionFunction13<T, P1, P2, P3, P4, P5, P6, P7, P8, P9, P10, P11, P12, P13, R>
 /** An extension function with introspection capabilities that takes 14 arguments. */
-public trait KExtensionFunction14<in T, in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, in P10, in P11, in P12, in P13, in P14, out R> : ExtensionFunction14<T, P1, P2, P3, P4, P5, P6, P7, P8, P9, P10, P11, P12, P13, P14, R>
+public interface KExtensionFunction14<in T, in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, in P10, in P11, in P12, in P13, in P14, out R> : ExtensionFunction14<T, P1, P2, P3, P4, P5, P6, P7, P8, P9, P10, P11, P12, P13, P14, R>
 /** An extension function with introspection capabilities that takes 15 arguments. */
-public trait KExtensionFunction15<in T, in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, in P10, in P11, in P12, in P13, in P14, in P15, out R> : ExtensionFunction15<T, P1, P2, P3, P4, P5, P6, P7, P8, P9, P10, P11, P12, P13, P14, P15, R>
+public interface KExtensionFunction15<in T, in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, in P10, in P11, in P12, in P13, in P14, in P15, out R> : ExtensionFunction15<T, P1, P2, P3, P4, P5, P6, P7, P8, P9, P10, P11, P12, P13, P14, P15, R>
 /** An extension function with introspection capabilities that takes 16 arguments. */
-public trait KExtensionFunction16<in T, in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, in P10, in P11, in P12, in P13, in P14, in P15, in P16, out R> : ExtensionFunction16<T, P1, P2, P3, P4, P5, P6, P7, P8, P9, P10, P11, P12, P13, P14, P15, P16, R>
+public interface KExtensionFunction16<in T, in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, in P10, in P11, in P12, in P13, in P14, in P15, in P16, out R> : ExtensionFunction16<T, P1, P2, P3, P4, P5, P6, P7, P8, P9, P10, P11, P12, P13, P14, P15, P16, R>
 /** An extension function with introspection capabilities that takes 17 arguments. */
-public trait KExtensionFunction17<in T, in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, in P10, in P11, in P12, in P13, in P14, in P15, in P16, in P17, out R> : ExtensionFunction17<T, P1, P2, P3, P4, P5, P6, P7, P8, P9, P10, P11, P12, P13, P14, P15, P16, P17, R>
+public interface KExtensionFunction17<in T, in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, in P10, in P11, in P12, in P13, in P14, in P15, in P16, in P17, out R> : ExtensionFunction17<T, P1, P2, P3, P4, P5, P6, P7, P8, P9, P10, P11, P12, P13, P14, P15, P16, P17, R>
 /** An extension function with introspection capabilities that takes 18 arguments. */
-public trait KExtensionFunction18<in T, in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, in P10, in P11, in P12, in P13, in P14, in P15, in P16, in P17, in P18, out R> : ExtensionFunction18<T, P1, P2, P3, P4, P5, P6, P7, P8, P9, P10, P11, P12, P13, P14, P15, P16, P17, P18, R>
+public interface KExtensionFunction18<in T, in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, in P10, in P11, in P12, in P13, in P14, in P15, in P16, in P17, in P18, out R> : ExtensionFunction18<T, P1, P2, P3, P4, P5, P6, P7, P8, P9, P10, P11, P12, P13, P14, P15, P16, P17, P18, R>
 /** An extension function with introspection capabilities that takes 19 arguments. */
-public trait KExtensionFunction19<in T, in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, in P10, in P11, in P12, in P13, in P14, in P15, in P16, in P17, in P18, in P19, out R> : ExtensionFunction19<T, P1, P2, P3, P4, P5, P6, P7, P8, P9, P10, P11, P12, P13, P14, P15, P16, P17, P18, P19, R>
+public interface KExtensionFunction19<in T, in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, in P10, in P11, in P12, in P13, in P14, in P15, in P16, in P17, in P18, in P19, out R> : ExtensionFunction19<T, P1, P2, P3, P4, P5, P6, P7, P8, P9, P10, P11, P12, P13, P14, P15, P16, P17, P18, P19, R>
 /** An extension function with introspection capabilities that takes 20 arguments. */
-public trait KExtensionFunction20<in T, in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, in P10, in P11, in P12, in P13, in P14, in P15, in P16, in P17, in P18, in P19, in P20, out R> : ExtensionFunction20<T, P1, P2, P3, P4, P5, P6, P7, P8, P9, P10, P11, P12, P13, P14, P15, P16, P17, P18, P19, P20, R>
+public interface KExtensionFunction20<in T, in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, in P10, in P11, in P12, in P13, in P14, in P15, in P16, in P17, in P18, in P19, in P20, out R> : ExtensionFunction20<T, P1, P2, P3, P4, P5, P6, P7, P8, P9, P10, P11, P12, P13, P14, P15, P16, P17, P18, P19, P20, R>
 /** An extension function with introspection capabilities that takes 21 arguments. */
-public trait KExtensionFunction21<in T, in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, in P10, in P11, in P12, in P13, in P14, in P15, in P16, in P17, in P18, in P19, in P20, in P21, out R> : ExtensionFunction21<T, P1, P2, P3, P4, P5, P6, P7, P8, P9, P10, P11, P12, P13, P14, P15, P16, P17, P18, P19, P20, P21, R>
+public interface KExtensionFunction21<in T, in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, in P10, in P11, in P12, in P13, in P14, in P15, in P16, in P17, in P18, in P19, in P20, in P21, out R> : ExtensionFunction21<T, P1, P2, P3, P4, P5, P6, P7, P8, P9, P10, P11, P12, P13, P14, P15, P16, P17, P18, P19, P20, P21, R>
 /** An extension function with introspection capabilities that takes 22 arguments. */
-public trait KExtensionFunction22<in T, in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, in P10, in P11, in P12, in P13, in P14, in P15, in P16, in P17, in P18, in P19, in P20, in P21, in P22, out R> : ExtensionFunction22<T, P1, P2, P3, P4, P5, P6, P7, P8, P9, P10, P11, P12, P13, P14, P15, P16, P17, P18, P19, P20, P21, P22, R>
+public interface KExtensionFunction22<in T, in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, in P10, in P11, in P12, in P13, in P14, in P15, in P16, in P17, in P18, in P19, in P20, in P21, in P22, out R> : ExtensionFunction22<T, P1, P2, P3, P4, P5, P6, P7, P8, P9, P10, P11, P12, P13, P14, P15, P16, P17, P18, P19, P20, P21, P22, R>
diff --git a/core/builtins/src/kotlin/reflect/KExtensionProperty.kt b/core/builtins/src/kotlin/reflect/KExtensionProperty.kt
index 4cefea1afa3..817e1c3c216 100644
--- a/core/builtins/src/kotlin/reflect/KExtensionProperty.kt
+++ b/core/builtins/src/kotlin/reflect/KExtensionProperty.kt
@@ -24,7 +24,7 @@ package kotlin.reflect
  * @param E the type of the extension receiver.
  * @param R the type of the property.
  */
-public trait KExtensionProperty<E, out R> : KProperty<R> {
+public interface KExtensionProperty<E, out R> : KProperty<R> {
     /**
      * Returns the current value of the property.
      *
@@ -36,7 +36,7 @@ public trait KExtensionProperty<E, out R> : KProperty<R> {
 /**
  * Represents an extension property declared as a `var`.
  */
-public trait KMutableExtensionProperty<E, R> : KExtensionProperty<E, R>, KMutableProperty<R> {
+public interface KMutableExtensionProperty<E, R> : KExtensionProperty<E, R>, KMutableProperty<R> {
     /**
      * Modifies the value of the property.
      *
diff --git a/core/builtins/src/kotlin/reflect/KFunctions.kt b/core/builtins/src/kotlin/reflect/KFunctions.kt
index c5397f68eb8..f79c41ae2b4 100644
--- a/core/builtins/src/kotlin/reflect/KFunctions.kt
+++ b/core/builtins/src/kotlin/reflect/KFunctions.kt
@@ -19,48 +19,48 @@
 package kotlin.reflect
 
 /** A function with introspection capabilities that takes 0 arguments. */
-public trait KFunction0<out R> : Function0<R>
+public interface KFunction0<out R> : Function0<R>
 /** A function with introspection capabilities that takes 1 argument. */
-public trait KFunction1<in P1, out R> : Function1<P1, R>
+public interface KFunction1<in P1, out R> : Function1<P1, R>
 /** A function with introspection capabilities that takes 2 arguments. */
-public trait KFunction2<in P1, in P2, out R> : Function2<P1, P2, R>
+public interface KFunction2<in P1, in P2, out R> : Function2<P1, P2, R>
 /** A function with introspection capabilities that takes 3 arguments. */
-public trait KFunction3<in P1, in P2, in P3, out R> : Function3<P1, P2, P3, R>
+public interface KFunction3<in P1, in P2, in P3, out R> : Function3<P1, P2, P3, R>
 /** A function with introspection capabilities that takes 4 arguments. */
-public trait KFunction4<in P1, in P2, in P3, in P4, out R> : Function4<P1, P2, P3, P4, R>
+public interface KFunction4<in P1, in P2, in P3, in P4, out R> : Function4<P1, P2, P3, P4, R>
 /** A function with introspection capabilities that takes 5 arguments. */
-public trait KFunction5<in P1, in P2, in P3, in P4, in P5, out R> : Function5<P1, P2, P3, P4, P5, R>
+public interface KFunction5<in P1, in P2, in P3, in P4, in P5, out R> : Function5<P1, P2, P3, P4, P5, R>
 /** A function with introspection capabilities that takes 6 arguments. */
-public trait KFunction6<in P1, in P2, in P3, in P4, in P5, in P6, out R> : Function6<P1, P2, P3, P4, P5, P6, R>
+public interface KFunction6<in P1, in P2, in P3, in P4, in P5, in P6, out R> : Function6<P1, P2, P3, P4, P5, P6, R>
 /** A function with introspection capabilities that takes 7 arguments. */
-public trait KFunction7<in P1, in P2, in P3, in P4, in P5, in P6, in P7, out R> : Function7<P1, P2, P3, P4, P5, P6, P7, R>
+public interface KFunction7<in P1, in P2, in P3, in P4, in P5, in P6, in P7, out R> : Function7<P1, P2, P3, P4, P5, P6, P7, R>
 /** A function with introspection capabilities that takes 8 arguments. */
-public trait KFunction8<in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, out R> : Function8<P1, P2, P3, P4, P5, P6, P7, P8, R>
+public interface KFunction8<in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, out R> : Function8<P1, P2, P3, P4, P5, P6, P7, P8, R>
 /** A function with introspection capabilities that takes 9 arguments. */
-public trait KFunction9<in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, out R> : Function9<P1, P2, P3, P4, P5, P6, P7, P8, P9, R>
+public interface KFunction9<in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, out R> : Function9<P1, P2, P3, P4, P5, P6, P7, P8, P9, R>
 /** A function with introspection capabilities that takes 10 arguments. */
-public trait KFunction10<in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, in P10, out R> : Function10<P1, P2, P3, P4, P5, P6, P7, P8, P9, P10, R>
+public interface KFunction10<in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, in P10, out R> : Function10<P1, P2, P3, P4, P5, P6, P7, P8, P9, P10, R>
 /** A function with introspection capabilities that takes 11 arguments. */
-public trait KFunction11<in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, in P10, in P11, out R> : Function11<P1, P2, P3, P4, P5, P6, P7, P8, P9, P10, P11, R>
+public interface KFunction11<in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, in P10, in P11, out R> : Function11<P1, P2, P3, P4, P5, P6, P7, P8, P9, P10, P11, R>
 /** A function with introspection capabilities that takes 12 arguments. */
-public trait KFunction12<in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, in P10, in P11, in P12, out R> : Function12<P1, P2, P3, P4, P5, P6, P7, P8, P9, P10, P11, P12, R>
+public interface KFunction12<in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, in P10, in P11, in P12, out R> : Function12<P1, P2, P3, P4, P5, P6, P7, P8, P9, P10, P11, P12, R>
 /** A function with introspection capabilities that takes 13 arguments. */
-public trait KFunction13<in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, in P10, in P11, in P12, in P13, out R> : Function13<P1, P2, P3, P4, P5, P6, P7, P8, P9, P10, P11, P12, P13, R>
+public interface KFunction13<in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, in P10, in P11, in P12, in P13, out R> : Function13<P1, P2, P3, P4, P5, P6, P7, P8, P9, P10, P11, P12, P13, R>
 /** A function with introspection capabilities that takes 14 arguments. */
-public trait KFunction14<in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, in P10, in P11, in P12, in P13, in P14, out R> : Function14<P1, P2, P3, P4, P5, P6, P7, P8, P9, P10, P11, P12, P13, P14, R>
+public interface KFunction14<in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, in P10, in P11, in P12, in P13, in P14, out R> : Function14<P1, P2, P3, P4, P5, P6, P7, P8, P9, P10, P11, P12, P13, P14, R>
 /** A function with introspection capabilities that takes 15 arguments. */
-public trait KFunction15<in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, in P10, in P11, in P12, in P13, in P14, in P15, out R> : Function15<P1, P2, P3, P4, P5, P6, P7, P8, P9, P10, P11, P12, P13, P14, P15, R>
+public interface KFunction15<in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, in P10, in P11, in P12, in P13, in P14, in P15, out R> : Function15<P1, P2, P3, P4, P5, P6, P7, P8, P9, P10, P11, P12, P13, P14, P15, R>
 /** A function with introspection capabilities that takes 16 arguments. */
-public trait KFunction16<in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, in P10, in P11, in P12, in P13, in P14, in P15, in P16, out R> : Function16<P1, P2, P3, P4, P5, P6, P7, P8, P9, P10, P11, P12, P13, P14, P15, P16, R>
+public interface KFunction16<in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, in P10, in P11, in P12, in P13, in P14, in P15, in P16, out R> : Function16<P1, P2, P3, P4, P5, P6, P7, P8, P9, P10, P11, P12, P13, P14, P15, P16, R>
 /** A function with introspection capabilities that takes 17 arguments. */
-public trait KFunction17<in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, in P10, in P11, in P12, in P13, in P14, in P15, in P16, in P17, out R> : Function17<P1, P2, P3, P4, P5, P6, P7, P8, P9, P10, P11, P12, P13, P14, P15, P16, P17, R>
+public interface KFunction17<in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, in P10, in P11, in P12, in P13, in P14, in P15, in P16, in P17, out R> : Function17<P1, P2, P3, P4, P5, P6, P7, P8, P9, P10, P11, P12, P13, P14, P15, P16, P17, R>
 /** A function with introspection capabilities that takes 18 arguments. */
-public trait KFunction18<in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, in P10, in P11, in P12, in P13, in P14, in P15, in P16, in P17, in P18, out R> : Function18<P1, P2, P3, P4, P5, P6, P7, P8, P9, P10, P11, P12, P13, P14, P15, P16, P17, P18, R>
+public interface KFunction18<in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, in P10, in P11, in P12, in P13, in P14, in P15, in P16, in P17, in P18, out R> : Function18<P1, P2, P3, P4, P5, P6, P7, P8, P9, P10, P11, P12, P13, P14, P15, P16, P17, P18, R>
 /** A function with introspection capabilities that takes 19 arguments. */
-public trait KFunction19<in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, in P10, in P11, in P12, in P13, in P14, in P15, in P16, in P17, in P18, in P19, out R> : Function19<P1, P2, P3, P4, P5, P6, P7, P8, P9, P10, P11, P12, P13, P14, P15, P16, P17, P18, P19, R>
+public interface KFunction19<in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, in P10, in P11, in P12, in P13, in P14, in P15, in P16, in P17, in P18, in P19, out R> : Function19<P1, P2, P3, P4, P5, P6, P7, P8, P9, P10, P11, P12, P13, P14, P15, P16, P17, P18, P19, R>
 /** A function with introspection capabilities that takes 20 arguments. */
-public trait KFunction20<in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, in P10, in P11, in P12, in P13, in P14, in P15, in P16, in P17, in P18, in P19, in P20, out R> : Function20<P1, P2, P3, P4, P5, P6, P7, P8, P9, P10, P11, P12, P13, P14, P15, P16, P17, P18, P19, P20, R>
+public interface KFunction20<in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, in P10, in P11, in P12, in P13, in P14, in P15, in P16, in P17, in P18, in P19, in P20, out R> : Function20<P1, P2, P3, P4, P5, P6, P7, P8, P9, P10, P11, P12, P13, P14, P15, P16, P17, P18, P19, P20, R>
 /** A function with introspection capabilities that takes 21 arguments. */
-public trait KFunction21<in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, in P10, in P11, in P12, in P13, in P14, in P15, in P16, in P17, in P18, in P19, in P20, in P21, out R> : Function21<P1, P2, P3, P4, P5, P6, P7, P8, P9, P10, P11, P12, P13, P14, P15, P16, P17, P18, P19, P20, P21, R>
+public interface KFunction21<in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, in P10, in P11, in P12, in P13, in P14, in P15, in P16, in P17, in P18, in P19, in P20, in P21, out R> : Function21<P1, P2, P3, P4, P5, P6, P7, P8, P9, P10, P11, P12, P13, P14, P15, P16, P17, P18, P19, P20, P21, R>
 /** A function with introspection capabilities that takes 22 arguments. */
-public trait KFunction22<in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, in P10, in P11, in P12, in P13, in P14, in P15, in P16, in P17, in P18, in P19, in P20, in P21, in P22, out R> : Function22<P1, P2, P3, P4, P5, P6, P7, P8, P9, P10, P11, P12, P13, P14, P15, P16, P17, P18, P19, P20, P21, P22, R>
+public interface KFunction22<in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, in P10, in P11, in P12, in P13, in P14, in P15, in P16, in P17, in P18, in P19, in P20, in P21, in P22, out R> : Function22<P1, P2, P3, P4, P5, P6, P7, P8, P9, P10, P11, P12, P13, P14, P15, P16, P17, P18, P19, P20, P21, P22, R>
diff --git a/core/builtins/src/kotlin/reflect/KMemberExtensionProperty.kt b/core/builtins/src/kotlin/reflect/KMemberExtensionProperty.kt
index 1841d37a7d5..a99c19a4f9f 100644
--- a/core/builtins/src/kotlin/reflect/KMemberExtensionProperty.kt
+++ b/core/builtins/src/kotlin/reflect/KMemberExtensionProperty.kt
@@ -26,7 +26,7 @@ package kotlin.reflect
  * @param E the type of the extension receiver.
  * @param R the type of the property.
  */
-public trait KMemberExtensionProperty<T : Any, E, out R> : KProperty<R> {
+public interface KMemberExtensionProperty<T : Any, E, out R> : KProperty<R> {
     /**
      * Returns the current value of the property.
      *
@@ -39,7 +39,7 @@ public trait KMemberExtensionProperty<T : Any, E, out R> : KProperty<R> {
 /**
  * Represents a `var` extension property declared in a class.
  */
-public trait KMutableMemberExtensionProperty<T : Any, E, R> : KMemberExtensionProperty<T, E, R>, KMutableProperty<R> {
+public interface KMutableMemberExtensionProperty<T : Any, E, R> : KMemberExtensionProperty<T, E, R>, KMutableProperty<R> {
     /**
      * Modifies the value of the property.
      *
diff --git a/core/builtins/src/kotlin/reflect/KMemberFunctions.kt b/core/builtins/src/kotlin/reflect/KMemberFunctions.kt
index f1676ca4be5..57f7e141423 100644
--- a/core/builtins/src/kotlin/reflect/KMemberFunctions.kt
+++ b/core/builtins/src/kotlin/reflect/KMemberFunctions.kt
@@ -19,48 +19,48 @@
 package kotlin.reflect
 
 /** A member function with introspection capabilities that takes 0 arguments. */
-public trait KMemberFunction0<in T, out R> : ExtensionFunction0<T, R>
+public interface KMemberFunction0<in T, out R> : ExtensionFunction0<T, R>
 /** A member function with introspection capabilities that takes 1 argument. */
-public trait KMemberFunction1<in T, in P1, out R> : ExtensionFunction1<T, P1, R>
+public interface KMemberFunction1<in T, in P1, out R> : ExtensionFunction1<T, P1, R>
 /** A member function with introspection capabilities that takes 2 arguments. */
-public trait KMemberFunction2<in T, in P1, in P2, out R> : ExtensionFunction2<T, P1, P2, R>
+public interface KMemberFunction2<in T, in P1, in P2, out R> : ExtensionFunction2<T, P1, P2, R>
 /** A member function with introspection capabilities that takes 3 arguments. */
-public trait KMemberFunction3<in T, in P1, in P2, in P3, out R> : ExtensionFunction3<T, P1, P2, P3, R>
+public interface KMemberFunction3<in T, in P1, in P2, in P3, out R> : ExtensionFunction3<T, P1, P2, P3, R>
 /** A member function with introspection capabilities that takes 4 arguments. */
-public trait KMemberFunction4<in T, in P1, in P2, in P3, in P4, out R> : ExtensionFunction4<T, P1, P2, P3, P4, R>
+public interface KMemberFunction4<in T, in P1, in P2, in P3, in P4, out R> : ExtensionFunction4<T, P1, P2, P3, P4, R>
 /** A member function with introspection capabilities that takes 5 arguments. */
-public trait KMemberFunction5<in T, in P1, in P2, in P3, in P4, in P5, out R> : ExtensionFunction5<T, P1, P2, P3, P4, P5, R>
+public interface KMemberFunction5<in T, in P1, in P2, in P3, in P4, in P5, out R> : ExtensionFunction5<T, P1, P2, P3, P4, P5, R>
 /** A member function with introspection capabilities that takes 6 arguments. */
-public trait KMemberFunction6<in T, in P1, in P2, in P3, in P4, in P5, in P6, out R> : ExtensionFunction6<T, P1, P2, P3, P4, P5, P6, R>
+public interface KMemberFunction6<in T, in P1, in P2, in P3, in P4, in P5, in P6, out R> : ExtensionFunction6<T, P1, P2, P3, P4, P5, P6, R>
 /** A member function with introspection capabilities that takes 7 arguments. */
-public trait KMemberFunction7<in T, in P1, in P2, in P3, in P4, in P5, in P6, in P7, out R> : ExtensionFunction7<T, P1, P2, P3, P4, P5, P6, P7, R>
+public interface KMemberFunction7<in T, in P1, in P2, in P3, in P4, in P5, in P6, in P7, out R> : ExtensionFunction7<T, P1, P2, P3, P4, P5, P6, P7, R>
 /** A member function with introspection capabilities that takes 8 arguments. */
-public trait KMemberFunction8<in T, in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, out R> : ExtensionFunction8<T, P1, P2, P3, P4, P5, P6, P7, P8, R>
+public interface KMemberFunction8<in T, in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, out R> : ExtensionFunction8<T, P1, P2, P3, P4, P5, P6, P7, P8, R>
 /** A member function with introspection capabilities that takes 9 arguments. */
-public trait KMemberFunction9<in T, in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, out R> : ExtensionFunction9<T, P1, P2, P3, P4, P5, P6, P7, P8, P9, R>
+public interface KMemberFunction9<in T, in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, out R> : ExtensionFunction9<T, P1, P2, P3, P4, P5, P6, P7, P8, P9, R>
 /** A member function with introspection capabilities that takes 10 arguments. */
-public trait KMemberFunction10<in T, in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, in P10, out R> : ExtensionFunction10<T, P1, P2, P3, P4, P5, P6, P7, P8, P9, P10, R>
+public interface KMemberFunction10<in T, in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, in P10, out R> : ExtensionFunction10<T, P1, P2, P3, P4, P5, P6, P7, P8, P9, P10, R>
 /** A member function with introspection capabilities that takes 11 arguments. */
-public trait KMemberFunction11<in T, in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, in P10, in P11, out R> : ExtensionFunction11<T, P1, P2, P3, P4, P5, P6, P7, P8, P9, P10, P11, R>
+public interface KMemberFunction11<in T, in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, in P10, in P11, out R> : ExtensionFunction11<T, P1, P2, P3, P4, P5, P6, P7, P8, P9, P10, P11, R>
 /** A member function with introspection capabilities that takes 12 arguments. */
-public trait KMemberFunction12<in T, in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, in P10, in P11, in P12, out R> : ExtensionFunction12<T, P1, P2, P3, P4, P5, P6, P7, P8, P9, P10, P11, P12, R>
+public interface KMemberFunction12<in T, in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, in P10, in P11, in P12, out R> : ExtensionFunction12<T, P1, P2, P3, P4, P5, P6, P7, P8, P9, P10, P11, P12, R>
 /** A member function with introspection capabilities that takes 13 arguments. */
-public trait KMemberFunction13<in T, in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, in P10, in P11, in P12, in P13, out R> : ExtensionFunction13<T, P1, P2, P3, P4, P5, P6, P7, P8, P9, P10, P11, P12, P13, R>
+public interface KMemberFunction13<in T, in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, in P10, in P11, in P12, in P13, out R> : ExtensionFunction13<T, P1, P2, P3, P4, P5, P6, P7, P8, P9, P10, P11, P12, P13, R>
 /** A member function with introspection capabilities that takes 14 arguments. */
-public trait KMemberFunction14<in T, in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, in P10, in P11, in P12, in P13, in P14, out R> : ExtensionFunction14<T, P1, P2, P3, P4, P5, P6, P7, P8, P9, P10, P11, P12, P13, P14, R>
+public interface KMemberFunction14<in T, in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, in P10, in P11, in P12, in P13, in P14, out R> : ExtensionFunction14<T, P1, P2, P3, P4, P5, P6, P7, P8, P9, P10, P11, P12, P13, P14, R>
 /** A member function with introspection capabilities that takes 15 arguments. */
-public trait KMemberFunction15<in T, in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, in P10, in P11, in P12, in P13, in P14, in P15, out R> : ExtensionFunction15<T, P1, P2, P3, P4, P5, P6, P7, P8, P9, P10, P11, P12, P13, P14, P15, R>
+public interface KMemberFunction15<in T, in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, in P10, in P11, in P12, in P13, in P14, in P15, out R> : ExtensionFunction15<T, P1, P2, P3, P4, P5, P6, P7, P8, P9, P10, P11, P12, P13, P14, P15, R>
 /** A member function with introspection capabilities that takes 16 arguments. */
-public trait KMemberFunction16<in T, in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, in P10, in P11, in P12, in P13, in P14, in P15, in P16, out R> : ExtensionFunction16<T, P1, P2, P3, P4, P5, P6, P7, P8, P9, P10, P11, P12, P13, P14, P15, P16, R>
+public interface KMemberFunction16<in T, in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, in P10, in P11, in P12, in P13, in P14, in P15, in P16, out R> : ExtensionFunction16<T, P1, P2, P3, P4, P5, P6, P7, P8, P9, P10, P11, P12, P13, P14, P15, P16, R>
 /** A member function with introspection capabilities that takes 17 arguments. */
-public trait KMemberFunction17<in T, in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, in P10, in P11, in P12, in P13, in P14, in P15, in P16, in P17, out R> : ExtensionFunction17<T, P1, P2, P3, P4, P5, P6, P7, P8, P9, P10, P11, P12, P13, P14, P15, P16, P17, R>
+public interface KMemberFunction17<in T, in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, in P10, in P11, in P12, in P13, in P14, in P15, in P16, in P17, out R> : ExtensionFunction17<T, P1, P2, P3, P4, P5, P6, P7, P8, P9, P10, P11, P12, P13, P14, P15, P16, P17, R>
 /** A member function with introspection capabilities that takes 18 arguments. */
-public trait KMemberFunction18<in T, in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, in P10, in P11, in P12, in P13, in P14, in P15, in P16, in P17, in P18, out R> : ExtensionFunction18<T, P1, P2, P3, P4, P5, P6, P7, P8, P9, P10, P11, P12, P13, P14, P15, P16, P17, P18, R>
+public interface KMemberFunction18<in T, in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, in P10, in P11, in P12, in P13, in P14, in P15, in P16, in P17, in P18, out R> : ExtensionFunction18<T, P1, P2, P3, P4, P5, P6, P7, P8, P9, P10, P11, P12, P13, P14, P15, P16, P17, P18, R>
 /** A member function with introspection capabilities that takes 19 arguments. */
-public trait KMemberFunction19<in T, in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, in P10, in P11, in P12, in P13, in P14, in P15, in P16, in P17, in P18, in P19, out R> : ExtensionFunction19<T, P1, P2, P3, P4, P5, P6, P7, P8, P9, P10, P11, P12, P13, P14, P15, P16, P17, P18, P19, R>
+public interface KMemberFunction19<in T, in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, in P10, in P11, in P12, in P13, in P14, in P15, in P16, in P17, in P18, in P19, out R> : ExtensionFunction19<T, P1, P2, P3, P4, P5, P6, P7, P8, P9, P10, P11, P12, P13, P14, P15, P16, P17, P18, P19, R>
 /** A member function with introspection capabilities that takes 20 arguments. */
-public trait KMemberFunction20<in T, in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, in P10, in P11, in P12, in P13, in P14, in P15, in P16, in P17, in P18, in P19, in P20, out R> : ExtensionFunction20<T, P1, P2, P3, P4, P5, P6, P7, P8, P9, P10, P11, P12, P13, P14, P15, P16, P17, P18, P19, P20, R>
+public interface KMemberFunction20<in T, in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, in P10, in P11, in P12, in P13, in P14, in P15, in P16, in P17, in P18, in P19, in P20, out R> : ExtensionFunction20<T, P1, P2, P3, P4, P5, P6, P7, P8, P9, P10, P11, P12, P13, P14, P15, P16, P17, P18, P19, P20, R>
 /** A member function with introspection capabilities that takes 21 arguments. */
-public trait KMemberFunction21<in T, in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, in P10, in P11, in P12, in P13, in P14, in P15, in P16, in P17, in P18, in P19, in P20, in P21, out R> : ExtensionFunction21<T, P1, P2, P3, P4, P5, P6, P7, P8, P9, P10, P11, P12, P13, P14, P15, P16, P17, P18, P19, P20, P21, R>
+public interface KMemberFunction21<in T, in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, in P10, in P11, in P12, in P13, in P14, in P15, in P16, in P17, in P18, in P19, in P20, in P21, out R> : ExtensionFunction21<T, P1, P2, P3, P4, P5, P6, P7, P8, P9, P10, P11, P12, P13, P14, P15, P16, P17, P18, P19, P20, P21, R>
 /** A member function with introspection capabilities that takes 22 arguments. */
-public trait KMemberFunction22<in T, in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, in P10, in P11, in P12, in P13, in P14, in P15, in P16, in P17, in P18, in P19, in P20, in P21, in P22, out R> : ExtensionFunction22<T, P1, P2, P3, P4, P5, P6, P7, P8, P9, P10, P11, P12, P13, P14, P15, P16, P17, P18, P19, P20, P21, P22, R>
+public interface KMemberFunction22<in T, in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, in P10, in P11, in P12, in P13, in P14, in P15, in P16, in P17, in P18, in P19, in P20, in P21, in P22, out R> : ExtensionFunction22<T, P1, P2, P3, P4, P5, P6, P7, P8, P9, P10, P11, P12, P13, P14, P15, P16, P17, P18, P19, P20, P21, P22, R>
diff --git a/core/builtins/src/kotlin/reflect/KMemberProperty.kt b/core/builtins/src/kotlin/reflect/KMemberProperty.kt
index c0a517ea10b..58c4d9f2ab1 100644
--- a/core/builtins/src/kotlin/reflect/KMemberProperty.kt
+++ b/core/builtins/src/kotlin/reflect/KMemberProperty.kt
@@ -23,7 +23,7 @@ package kotlin.reflect
  *          Must be derived either from a class declaring this property, or any subclass of that class.
  * @param R the type of the property.
  */
-public trait KMemberProperty<T : Any, out R> : KProperty<R> {
+public interface KMemberProperty<T : Any, out R> : KProperty<R> {
     /**
      * Returns the current value of the property.
      *
@@ -35,7 +35,7 @@ public trait KMemberProperty<T : Any, out R> : KProperty<R> {
 /**
  * Represents a `var` property declared in a class.
  */
-public trait KMutableMemberProperty<T : Any, R> : KMemberProperty<T, R>, KMutableProperty<R> {
+public interface KMutableMemberProperty<T : Any, R> : KMemberProperty<T, R>, KMutableProperty<R> {
     /**
      * Modifies the value of the property.
      *
diff --git a/core/builtins/src/kotlin/reflect/KPackage.kt b/core/builtins/src/kotlin/reflect/KPackage.kt
index b0161bded0d..1f26a51565b 100644
--- a/core/builtins/src/kotlin/reflect/KPackage.kt
+++ b/core/builtins/src/kotlin/reflect/KPackage.kt
@@ -19,4 +19,4 @@ package kotlin.reflect
 /**
  * Represents a package and provides introspection capabilities.
  */
-public trait KPackage
+public interface KPackage
diff --git a/core/builtins/src/kotlin/reflect/KProperty.kt b/core/builtins/src/kotlin/reflect/KProperty.kt
index 311409a0a10..10f4a3508a2 100644
--- a/core/builtins/src/kotlin/reflect/KProperty.kt
+++ b/core/builtins/src/kotlin/reflect/KProperty.kt
@@ -24,9 +24,9 @@ package kotlin.reflect
  *
  * @param R the type of the property.
  */
-public trait KProperty<out R> : KCallable<R>
+public interface KProperty<out R> : KCallable<R>
 
 /**
  * Represents a property declared as a `var`.
  */
-public trait KMutableProperty<R> : KProperty<R>
+public interface KMutableProperty<R> : KProperty<R>
diff --git a/core/builtins/src/kotlin/reflect/KTopLevelExtensionProperty.kt b/core/builtins/src/kotlin/reflect/KTopLevelExtensionProperty.kt
index 229c915942b..3381b037182 100644
--- a/core/builtins/src/kotlin/reflect/KTopLevelExtensionProperty.kt
+++ b/core/builtins/src/kotlin/reflect/KTopLevelExtensionProperty.kt
@@ -19,9 +19,9 @@ package kotlin.reflect
 /**
  * Represents an extension property declared in a package.
  */
-public trait KTopLevelExtensionProperty<E, out R> : KExtensionProperty<E, R>, KTopLevelProperty<R>
+public interface KTopLevelExtensionProperty<E, out R> : KExtensionProperty<E, R>, KTopLevelProperty<R>
 
 /**
  * Represents a package extension property declared as a `var`.
  */
-public trait KMutableTopLevelExtensionProperty<E, R> : KTopLevelExtensionProperty<E, R>, KMutableExtensionProperty<E, R>, KMutableTopLevelProperty<R>
+public interface KMutableTopLevelExtensionProperty<E, R> : KTopLevelExtensionProperty<E, R>, KMutableExtensionProperty<E, R>, KMutableTopLevelProperty<R>
diff --git a/core/builtins/src/kotlin/reflect/KTopLevelProperty.kt b/core/builtins/src/kotlin/reflect/KTopLevelProperty.kt
index 49f4ad5281e..597e831325f 100644
--- a/core/builtins/src/kotlin/reflect/KTopLevelProperty.kt
+++ b/core/builtins/src/kotlin/reflect/KTopLevelProperty.kt
@@ -19,9 +19,9 @@ package kotlin.reflect
 /**
  * Represents a property declared in a package.
  */
-public trait KTopLevelProperty<out R> : KProperty<R>
+public interface KTopLevelProperty<out R> : KProperty<R>
 
 /**
  * Represents a package property declared as a `var`.
  */
-public trait KMutableTopLevelProperty<R> : KTopLevelProperty<R>, KMutableProperty<R>
+public interface KMutableTopLevelProperty<R> : KTopLevelProperty<R>, KMutableProperty<R>
diff --git a/core/builtins/src/kotlin/reflect/KTopLevelVariable.kt b/core/builtins/src/kotlin/reflect/KTopLevelVariable.kt
index 9df6e519008..39b8856ac66 100644
--- a/core/builtins/src/kotlin/reflect/KTopLevelVariable.kt
+++ b/core/builtins/src/kotlin/reflect/KTopLevelVariable.kt
@@ -19,9 +19,9 @@ package kotlin.reflect
 /**
  * Represents a variable declared in a package.
  */
-public trait KTopLevelVariable<out R> : KVariable<R>, KTopLevelProperty<R>
+public interface KTopLevelVariable<out R> : KVariable<R>, KTopLevelProperty<R>
 
 /**
  * Represents a package variable declared as a `var`.
  */
-public trait KMutableTopLevelVariable<R> : KTopLevelVariable<R>, KMutableVariable<R>, KMutableTopLevelProperty<R>
+public interface KMutableTopLevelVariable<R> : KTopLevelVariable<R>, KMutableVariable<R>, KMutableTopLevelProperty<R>
diff --git a/core/builtins/src/kotlin/reflect/KVariable.kt b/core/builtins/src/kotlin/reflect/KVariable.kt
index ff1fec7a4b2..100e149a5c0 100644
--- a/core/builtins/src/kotlin/reflect/KVariable.kt
+++ b/core/builtins/src/kotlin/reflect/KVariable.kt
@@ -21,7 +21,7 @@ package kotlin.reflect
  * Such property is either originally declared in a receiverless context such as a package,
  * or has the receiver bound to it.
  */
-public trait KVariable<out R> : KProperty<R> {
+public interface KVariable<out R> : KProperty<R> {
     /**
      * Returns the current value of the variable.
      */
@@ -31,7 +31,7 @@ public trait KVariable<out R> : KProperty<R> {
 /**
  * Represents a variable declared as a `var`.
  */
-public trait KMutableVariable<R> : KVariable<R>, KMutableProperty<R> {
+public interface KMutableVariable<R> : KVariable<R>, KMutableProperty<R> {
     /**
      * Modifies the value of the variable.
      *
diff --git a/generators/src/org/jetbrains/kotlin/generators/builtins/functions.kt b/generators/src/org/jetbrains/kotlin/generators/builtins/functions.kt
index 0378588c559..04557ad057a 100644
--- a/generators/src/org/jetbrains/kotlin/generators/builtins/functions.kt
+++ b/generators/src/org/jetbrains/kotlin/generators/builtins/functions.kt
@@ -65,7 +65,7 @@ class GenerateFunctions(out: PrintWriter, val kind: FunctionKind) : BuiltInsSour
     override fun generateBody() {
         for (i in 0..MAX_PARAM_COUNT) {
             generateDocumentation(i)
-            out.print("public trait " + kind.getClassName(i))
+            out.print("public interface " + kind.getClassName(i))
             generateTypeParameters(i, true)
             generateSuperClass(i)
             generateFunctionClassBody(i)
diff --git a/libraries/stdlib/src/kotlin/collections/Sequence.kt b/libraries/stdlib/src/kotlin/collections/Sequence.kt
index 581564795c2..40a28a7cfcf 100644
--- a/libraries/stdlib/src/kotlin/collections/Sequence.kt
+++ b/libraries/stdlib/src/kotlin/collections/Sequence.kt
@@ -4,7 +4,7 @@ import java.util.Enumeration
 import java.util.NoSuchElementException
 
 deprecated("Use Sequence<T> instead.")
-public trait Stream<out T> {
+public interface Stream<out T> {
     /**
      * Returns an iterator that returns the values from the sequence.
      */
@@ -17,7 +17,7 @@ public trait Stream<out T> {
  *
  * @param T the type of elements in the sequence.
  */
-public trait Sequence<out T> : Stream<T>
+public interface Sequence<out T> : Stream<T>
 
 public fun<T> Stream<T>.toSequence(): Sequence<T> = object : Sequence<T> {
     override fun iterator(): Iterator<T> = this@toSequence.iterator()
diff --git a/libraries/stdlib/src/kotlin/io/Console.kt b/libraries/stdlib/src/kotlin/io/Console.kt
index 099daab0b6f..261d8ca271a 100644
--- a/libraries/stdlib/src/kotlin/io/Console.kt
+++ b/libraries/stdlib/src/kotlin/io/Console.kt
@@ -126,7 +126,7 @@ public fun println() {
 
 // Since System.in can change its value on the course of program running,
 // we should always delegate to current value and cannot just pass it to InputStreamReader constructor.
-// We could use "by" implementation, but we can only use "by" with traits and InputStream is abstract class.
+// We could use "by" implementation, but we can only use "by" with interfaces and InputStream is abstract class.
 private val stdin: BufferedReader = BufferedReader(InputStreamReader(object : InputStream() {
     public override fun read(): Int {
         return System.`in`.read()
diff --git a/libraries/stdlib/src/kotlin/properties/Delegation.kt b/libraries/stdlib/src/kotlin/properties/Delegation.kt
index 6f22c7ef4f9..5a0191cc585 100644
--- a/libraries/stdlib/src/kotlin/properties/Delegation.kt
+++ b/libraries/stdlib/src/kotlin/properties/Delegation.kt
@@ -1,13 +1,13 @@
 package kotlin.properties
 
 /**
- * Base trait that can be used for implementing property delegates of read-only properties. This is provided only for
- * convenience; you don't have to extend this trait as long as your property delegate has methods with the same
+ * Base interface that can be used for implementing property delegates of read-only properties. This is provided only for
+ * convenience; you don't have to extend this interface as long as your property delegate has methods with the same
  * signatures.
  * @param R the type of object which owns the delegated property.
  * @param T the type of the property value.
  */
-public trait ReadOnlyProperty<in R, out T> {
+public interface ReadOnlyProperty<in R, out T> {
     /**
      * Returns the value of the property for the given object.
      * @param thisRef the object for which the value is requested.
@@ -18,13 +18,13 @@ public trait ReadOnlyProperty<in R, out T> {
 }
 
 /**
- * Base trait that can be used for implementing property delegates of read-only properties. This is provided only for
- * convenience; you don't have to extend this trait as long as your property delegate has methods with the same
+ * Base interface that can be used for implementing property delegates of read-only properties. This is provided only for
+ * convenience; you don't have to extend this interface as long as your property delegate has methods with the same
  * signatures.
  * @param R the type of object which owns the delegated property.
  * @param T the type of the property value.
  */
-public trait ReadWriteProperty<in R, T> {
+public interface ReadWriteProperty<in R, T> {
     /**
      * Returns the value of the property for the given object.
      * @param thisRef the object for which the value is requested.
diff --git a/libraries/stdlib/src/kotlin/properties/Properties.kt b/libraries/stdlib/src/kotlin/properties/Properties.kt
index 8a22e37bb9c..d93c08243ed 100644
--- a/libraries/stdlib/src/kotlin/properties/Properties.kt
+++ b/libraries/stdlib/src/kotlin/properties/Properties.kt
@@ -14,7 +14,7 @@ public class ChangeEvent(
 }
 
 deprecated("This class is part of an old, incomplete and suboptimal design of change notifications and is going to be removed")
-public trait ChangeListener {
+public interface ChangeListener {
     public fun onPropertyChange(event: ChangeEvent): Unit
 }
 
diff --git a/libraries/stdlib/src/kotlin/template/Templates.kt b/libraries/stdlib/src/kotlin/template/Templates.kt
index b8820b645f7..7505d956b19 100644
--- a/libraries/stdlib/src/kotlin/template/Templates.kt
+++ b/libraries/stdlib/src/kotlin/template/Templates.kt
@@ -86,8 +86,8 @@ public fun StringTemplate.toHtml(formatter: HtmlFormatter = HtmlFormatter()): St
  * how to format values for a particular [[Locale]] such as with the [[LocaleFormatter]] or
  * to escape particular characters in different output formats such as [[HtmlFormatter]
  */
-deprecated("This trait is part of an experimental implementation of string templates and is going to be removed")
-public trait Formatter {
+deprecated("This interface is part of an experimental implementation of string templates and is going to be removed")
+public interface Formatter {
     public fun format(buffer: Appendable, value: Any?): Unit
 }
 
diff --git a/libraries/stdlib/src/kotlin/test/Test.kt b/libraries/stdlib/src/kotlin/test/Test.kt
index 2807497b414..d0f4e757ea6 100644
--- a/libraries/stdlib/src/kotlin/test/Test.kt
+++ b/libraries/stdlib/src/kotlin/test/Test.kt
@@ -92,7 +92,7 @@ public fun fails(block: () -> Unit): Throwable? {
  * Abstracts the logic for performing assertions. Specific implementations of [Asserter] can use JUnit
  * or TestNG assertion facilities.
  */
-public trait Asserter {
+public interface Asserter {
     /**
      * Asserts that the specified value is true.
      *
diff --git a/libraries/stdlib/src/kotlin/text/regex/Regex.kt b/libraries/stdlib/src/kotlin/text/regex/Regex.kt
index 8c534788024..34329761b9f 100644
--- a/libraries/stdlib/src/kotlin/text/regex/Regex.kt
+++ b/libraries/stdlib/src/kotlin/text/regex/Regex.kt
@@ -17,7 +17,7 @@
 package kotlin.text
 
 /** Represents a collection of captured groups in a single match. */
-public trait MatchGroupCollection : Collection<MatchGroup?> {
+public interface MatchGroupCollection : Collection<MatchGroup?> {
 
     /** Returns a group with the specified [index]
      *
@@ -34,7 +34,7 @@ public trait MatchGroupCollection : Collection<MatchGroup?> {
 /**
  * Represents the results from a single regular expression match.
  */
-public trait MatchResult {
+public interface MatchResult {
     /** The range of indices in the original string where match was captured. */
     public val range: IntRange
     /** The substring from the input string captured by this match. */
diff --git a/libraries/stdlib/src/kotlin/text/regex/RegexJVM.kt b/libraries/stdlib/src/kotlin/text/regex/RegexJVM.kt
index f0edff887ee..70d28c97c4f 100644
--- a/libraries/stdlib/src/kotlin/text/regex/RegexJVM.kt
+++ b/libraries/stdlib/src/kotlin/text/regex/RegexJVM.kt
@@ -19,7 +19,7 @@ package kotlin.text
 import java.util.regex.Pattern
 import java.util.regex.Matcher
 
-private trait FlagEnum {
+private interface FlagEnum {
     public val value: Int
     public val mask: Int
 }
diff --git a/libraries/stdlib/test/properties/delegation/DelegationTest.kt b/libraries/stdlib/test/properties/delegation/DelegationTest.kt
index 157f668e3df..4f78f3647c6 100644
--- a/libraries/stdlib/test/properties/delegation/DelegationTest.kt
+++ b/libraries/stdlib/test/properties/delegation/DelegationTest.kt
@@ -4,7 +4,7 @@ import org.junit.Test as test
 import kotlin.test.*
 import kotlin.properties.*
 
-trait WithBox {
+interface WithBox {
     fun box(): String
 }
 
diff --git a/libraries/tools/kotlin-gradle-plugin-api/src/main/kotlin/org/jetbrains/kotlin/gradle/plugin/KotlinGradleSubplugin.kt b/libraries/tools/kotlin-gradle-plugin-api/src/main/kotlin/org/jetbrains/kotlin/gradle/plugin/KotlinGradleSubplugin.kt
index 971b4a75215..fda340afdef 100644
--- a/libraries/tools/kotlin-gradle-plugin-api/src/main/kotlin/org/jetbrains/kotlin/gradle/plugin/KotlinGradleSubplugin.kt
+++ b/libraries/tools/kotlin-gradle-plugin-api/src/main/kotlin/org/jetbrains/kotlin/gradle/plugin/KotlinGradleSubplugin.kt
@@ -21,7 +21,7 @@ import org.gradle.api.tasks.compile.AbstractCompile
 
 public class SubpluginOption(val key: String, val value: String)
 
-public trait KotlinGradleSubplugin {
+public interface KotlinGradleSubplugin {
     public fun getExtraArguments(project: Project, task: AbstractCompile): List<SubpluginOption>?
     public fun getPluginName(): String
     public fun getGroupName(): String
diff --git a/libraries/tools/kotlin-gradle-plugin/src/main/kotlin/org/jetbrains/kotlin/gradle/internal/KotlinSourceSet.kt b/libraries/tools/kotlin-gradle-plugin/src/main/kotlin/org/jetbrains/kotlin/gradle/internal/KotlinSourceSet.kt
index eb385c68c68..79c74d31a5b 100644
--- a/libraries/tools/kotlin-gradle-plugin/src/main/kotlin/org/jetbrains/kotlin/gradle/internal/KotlinSourceSet.kt
+++ b/libraries/tools/kotlin-gradle-plugin/src/main/kotlin/org/jetbrains/kotlin/gradle/internal/KotlinSourceSet.kt
@@ -6,7 +6,7 @@ import org.gradle.api.internal.file.FileResolver
 import org.gradle.api.internal.file.DefaultSourceDirectorySet
 import org.gradle.util.ConfigureUtil
 
-trait KotlinSourceSet {
+interface KotlinSourceSet {
 
     fun getKotlin(): SourceDirectorySet
     fun kotlin(configureClosure: Closure<Any?>?): KotlinSourceSet
diff --git a/libraries/tools/kotlin-gradle-plugin/src/test/resources/testProject/suppressWarningsAndVersion/src/helloWorld.kt b/libraries/tools/kotlin-gradle-plugin/src/test/resources/testProject/suppressWarningsAndVersion/src/helloWorld.kt
index b97b1e74260..46efcd61cca 100644
--- a/libraries/tools/kotlin-gradle-plugin/src/test/resources/testProject/suppressWarningsAndVersion/src/helloWorld.kt
+++ b/libraries/tools/kotlin-gradle-plugin/src/test/resources/testProject/suppressWarningsAndVersion/src/helloWorld.kt
@@ -7,7 +7,7 @@ fun foo(p: Int??) {
 
 }
 
-trait T {
+interface T {
     abstract fun foo()
 }
 
diff --git a/libraries/tools/kotlin-maven-plugin-test/src/it/test-js-suppressWarnings/src/main/kotlin/org/jetbrains/HelloWorld.kt b/libraries/tools/kotlin-maven-plugin-test/src/it/test-js-suppressWarnings/src/main/kotlin/org/jetbrains/HelloWorld.kt
index a2dabbd8903..5f51a3cc290 100644
--- a/libraries/tools/kotlin-maven-plugin-test/src/it/test-js-suppressWarnings/src/main/kotlin/org/jetbrains/HelloWorld.kt
+++ b/libraries/tools/kotlin-maven-plugin-test/src/it/test-js-suppressWarnings/src/main/kotlin/org/jetbrains/HelloWorld.kt
@@ -7,7 +7,7 @@ fun foo(p: Int??) {
 
 }
 
-trait T {
+interface T {
     abstract fun foo()
 }
 
diff --git a/libraries/tools/kotlin-maven-plugin-test/src/it/test-suppressWarnings/src/main/kotlin/org/jetbrains/HelloWorld.kt b/libraries/tools/kotlin-maven-plugin-test/src/it/test-suppressWarnings/src/main/kotlin/org/jetbrains/HelloWorld.kt
index 1db88783020..50eaad2ed93 100644
--- a/libraries/tools/kotlin-maven-plugin-test/src/it/test-suppressWarnings/src/main/kotlin/org/jetbrains/HelloWorld.kt
+++ b/libraries/tools/kotlin-maven-plugin-test/src/it/test-suppressWarnings/src/main/kotlin/org/jetbrains/HelloWorld.kt
@@ -7,7 +7,7 @@ fun foo(p: Int??) {
 
 }
 
-trait T {
+interface T {
     abstract fun foo()
 }
 
diff --git a/libraries/tools/kotlin-stdlib-gen/src/generators/GenerateJavaScriptStubs.kt b/libraries/tools/kotlin-stdlib-gen/src/generators/GenerateJavaScriptStubs.kt
index 2819c3d9b9d..3791a285b5c 100644
--- a/libraries/tools/kotlin-stdlib-gen/src/generators/GenerateJavaScriptStubs.kt
+++ b/libraries/tools/kotlin-stdlib-gen/src/generators/GenerateJavaScriptStubs.kt
@@ -87,7 +87,7 @@ $imports
             val interfaces = klass.getInterfaces()
             val extends = if (interfaces != null && interfaces.size == 1) ": ${interfaces[0]?.getSimpleName()}" else ""
 
-            println("native public trait ${klass.getSimpleName()}$extends {")
+            println("native public interface ${klass.getSimpleName()}$extends {")
 
             val methods = klass.getDeclaredMethods().sortBy { it.getName()!! }
             if (methods != null) {