diff --git a/examples/src/array/MutableArray.jetl b/examples/src/array/MutableArray.jetl
new file mode 100644
index 00000000000..a2c0dba2e90
--- /dev/null
+++ b/examples/src/array/MutableArray.jetl
@@ -0,0 +1,13 @@
+/**
+  These declarations are "shallow" in the sense that they are not really compiled, only the type-checker uses them
+*/
+
+interface class ReadOnlyArray<out T> : ISized {
+  [operator] fun get(index : Int) : T
+}
+
+interface class WriteOnlyArray<in T> : ISized { // This is needed to keep IIterator's <T> covariant 
+  [operator] fun set(index : Int, value : T)
+}
+
+class MutableArray<T> : ReadOnlyArray<T>, WriteOnlyArray<T> {...}
\ No newline at end of file
diff --git a/examples/src/collections/IIterator.jetl b/examples/src/collections/IIterator.jetl
index 7717e94062f..31469b269b3 100644
--- a/examples/src/collections/IIterator.jetl
+++ b/examples/src/collections/IIterator.jetl
@@ -1,4 +1,25 @@
 interface class IIterator<out T> {
   fun next() : T
   val hasNext : Boolean
+
+  fun toArray(buffer : WriteOnlyArray<T>) : Int { // T is still an in-parameter
+    return fillBuffer(buffer, 0, buffer.size)
+  }
+
+  fun toArray(buffer : WriteOnlyArray<T>, from : Int, length : Int) : Int { // T is still an in-parameter
+    if (from < 0 || from > buffer.lastIndex || length < 0 || length > buffer.size - from) {
+      throw IndexOutOfBoundsException();
+    }
+
+    if (len == 0) return 0;
+
+    var count = 0;
+    for (i in [from .. from + length - 1]) {
+      if (!hasNext)
+        return count
+      buffer[i] = next()
+      count++
+    }
+    return count
+  }
 }
diff --git a/examples/src/collections/IList.jetl b/examples/src/collections/IList.jetl
index 9e03010ae58..70f1e2cfb2e 100644
--- a/examples/src/collections/IList.jetl
+++ b/examples/src/collections/IList.jetl
@@ -1,4 +1,4 @@
-interface class IList<out T> : IIterable<T>, ISizable {
+interface class IList<out T> : IIterable<T>, ISized {
   [operator] fun get(index : Int) : T
   val isEmpty : Boolean
 }
\ No newline at end of file
diff --git a/examples/src/collections/IMutableIterator.jetl b/examples/src/collections/IMutableIterator.jetl
index c00e01c3eaa..775980ccedc 100644
--- a/examples/src/collections/IMutableIterator.jetl
+++ b/examples/src/collections/IMutableIterator.jetl
@@ -1,3 +1,13 @@
 interface class IMutableIterator<out T> : IIterator<T> {
   fun remove() : T
+
+/*
+  Considerations:
+    pro: why not + non iteration breaking
+    con: counter-intuitive for, e.g., TreeSet
+
+
+  fun addBefore(item : T) : Boolean
+  fun addAfter(item : T) : Boolean
+*/
 }
\ No newline at end of file
diff --git a/examples/src/collections/LinkedList.jetl b/examples/src/collections/LinkedList.jetl
index ca16db4d89a..43be0302cea 100644
--- a/examples/src/collections/LinkedList.jetl
+++ b/examples/src/collections/LinkedList.jetl
@@ -15,14 +15,14 @@ class LinkedList<T> : IMutableList<T> {
     if (index == 0) {
       newItem.next = head
       head = newItem
-      if (tail == null) {
+      if (tail === null) {
         tail = head
       }
     } else {
       var insertAfter = itemAt(index)
       newItem.next = insertAfter.next
       insertAfter.next = newItem
-      if (tail == insertAfter) {
+      if (tail === insertAfter) {
         tail = newItem
       }
     }
@@ -37,13 +37,13 @@ class LinkedList<T> : IMutableList<T> {
   override fun remove(index : Int) : T {
     checkIndex(index)
     val item = itemAt(index)
-    if (item == head) {
+    if (item === head) {
       head = item.next
-      if (head == null)
+      if (head === null)
         tail= null
     } else {
       item.previous.next = item.next
-      if (item.next == null) {
+      if (item.next === null) {
         item.next.previous = item.previous
       } else {
         tail = tail.previous
diff --git a/examples/src/io/IOSamples.jetl b/examples/src/io/IOSamples.jetl
new file mode 100644
index 00000000000..8f0b10ce79f
--- /dev/null
+++ b/examples/src/io/IOSamples.jetl
@@ -0,0 +1,62 @@
+interface class IAdder<in T> {
+  fun add(item : T) : Boolean
+}
+
+interface class ICloseable {
+  fun close()
+}
+
+abstract class JavaCloseableWrapper(closeable : java.io.Closeable) : ICloseable(closeable)
+
+fun streamCopy<T>(from : IIterable<T>, to : IAdder<T>) {
+  for (item in from) t.add(item)
+}
+
+class FileInput : IIterator<Byte>, JavaCloseableWrapper {
+  private val stream : InputStream
+  private var next : Int
+  private var nextUsed = false
+
+  this(file : File) : JavaCloseableWrapper(stream) { // implicitly throws IOException
+    stream = FileInputStream(file) // throws IOException
+  }
+
+  override fun next() {
+    if (!nextUsed) {
+      nextUsed = true
+      return next.as<Byte>
+    }
+    return
+  }
+  
+  override val hasNext {
+    get() { // implicitly throws IOException
+      if (nextUsed && next != -1) {
+        nextUsed = false
+        next = stream.read() // throws IOException
+      }
+      return next != -1        
+    }
+  }
+}
+
+class FileOutput throws IOException : IAdder<Byte>, JavaCloseableWrapper {
+  private val stream : OutputStream
+
+  this(file : File) : JavaCloseableWrapper(stream) {
+    stream = FileOutputStream(file)
+  }
+
+  override fun add(item : Byte) {
+    stream.write(item)
+  }
+}
+
+fun example() { // this does not rethrow, no appropriate parameters given
+
+  val f1 : File = ...
+  val f2 : File = ...
+
+  streamCopy(FileInput(f1), f2) // throws IOException, you must catch or rethrow explicitly
+
+}
\ No newline at end of file
diff --git a/examples/src/io/IOSamplesChEx.jetl b/examples/src/io/IOSamplesChEx.jetl
new file mode 100644
index 00000000000..087f8ed7db7
--- /dev/null
+++ b/examples/src/io/IOSamplesChEx.jetl
@@ -0,0 +1,71 @@
+interface class IIterable<T> throws <E> {
+  fun next() : T // implicitly throws  <E>
+  val hasNext : Boolean // implicitly throws <E>, but actually may NOT!!!
+}
+
+interface class IAdder<T> throws <E> {
+  fun add(item : T) : Boolean // implicitly throws <E>
+}
+
+interface class ICloseable throws <E> {
+  fun close()
+}
+
+abstract class JavaCloseableWrapper(closeable : java.io.Closeable) throws <IOException> : ICloseable { // Maybe we can delegate here
+  override fun close() {
+    closeable.close()
+  }
+}
+
+fun streamCopy<T>(from : IIterable<T>, to : IAdder<T>) { // implicitly rethrows
+  for (item in from) t.add(item) // both implicitly throw <E>
+}
+
+class FileInput throws <IOException> : IIterable<Byte>, JavaCloseableWrapper {
+  private val stream : InputStream
+  private var next : Int
+  private var nextUsed = false
+
+  this(file : File) : JavaCloseableWrapper(stream) { // implicitly throws IOException
+    stream = FileInputStream(file) // throws IOException
+  }
+
+  override fun next() {
+    if (!nextUsed) {
+      nextUsed = true
+      return next.as<Byte>
+    }
+    return
+  }
+  
+  override val hasNext {
+    get() { // implicitly throws IOException
+      if (nextUsed && next != -1) {
+        nextUsed = false
+        next = stream.read() // throws IOException
+      }
+      return next != -1        
+    }
+  }
+}
+
+class FileOutput throws IOException : IAdder<Byte>, JavaCloseableWrapper {
+  private val stream : OutputStream
+
+  this(file : File) : JavaCloseableWrapper(stream) {
+    stream = FileOutputStream(file)
+  }
+
+  override fun add(item : Byte) {
+    stream.write(item)
+  }
+}
+
+fun example() { // this does not rethrow, no appropriate parameters given
+
+  val f1 : File = ...
+  val f2 : File = ...
+
+  streamCopy(FileInput(f1), f2) // throws IOException, you must catch or rethrow explicitly
+
+}
\ No newline at end of file