diff --git a/compiler/frontend/src/org/jetbrains/jet/lang/resolve/calls/inference/TypeBounds.java b/compiler/frontend/src/org/jetbrains/jet/lang/resolve/calls/inference/TypeBounds.java
deleted file mode 100644
index ac460f43026..00000000000
--- a/compiler/frontend/src/org/jetbrains/jet/lang/resolve/calls/inference/TypeBounds.java
+++ /dev/null
@@ -1,79 +0,0 @@
-/*
- * Copyright 2010-2012 JetBrains s.r.o.
- *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- * http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
- */
-
-package org.jetbrains.jet.lang.resolve.calls.inference;
-
-import com.google.common.collect.Sets;
-import org.jetbrains.jet.lang.descriptors.TypeParameterDescriptor;
-import org.jetbrains.jet.lang.types.JetType;
-import org.jetbrains.jet.lang.types.Variance;
-
-import java.util.Set;
-
-/**
- * @author svtk
- */
-public class TypeBounds {
-    private final Variance variance;
-    private final Set<JetType> upperBounds = Sets.newLinkedHashSet();
-    private final Set<JetType> lowerBounds = Sets.newLinkedHashSet();
-    private final Set<JetType> exactValues = Sets.newLinkedHashSet();
-
-    public TypeBounds(Variance variance) {
-        this.variance = variance;
-    }
-
-    public Variance getVariance() {
-        return variance;
-    }
-
-    public void addUpperBound(JetType upperBound) {
-        upperBounds.add(upperBound);
-    }
-
-    public void addLowerBound(JetType lowerBound) {
-        lowerBounds.add(lowerBound);
-    }
-
-    public Set<JetType> getUpperBounds() {
-        return upperBounds;
-    }
-
-    public Set<JetType> getLowerBounds() {
-        return lowerBounds;
-    }
-
-    public void setExactValue(JetType exactType) {
-        exactValues.add(exactType);
-    }
-
-    public Set<JetType> getExactValues() {
-        return exactValues;
-    }
-
-    public boolean isEmpty() {
-        return lowerBounds.isEmpty() && upperBounds.isEmpty() && exactValues.isEmpty();
-    }
-
-    @Override
-    public String toString() {
-        return "TypeBounds{" +
-               "upperBounds=" + upperBounds +
-               ", lowerBounds=" + lowerBounds +
-               ", exactValues=" + exactValues +
-               '}';
-    }
-}
diff --git a/compiler/frontend/src/org/jetbrains/jet/lang/resolve/calls/inference/TypeConstraintsImpl.java b/compiler/frontend/src/org/jetbrains/jet/lang/resolve/calls/inference/TypeConstraintsImpl.java
new file mode 100644
index 00000000000..62430383547
--- /dev/null
+++ b/compiler/frontend/src/org/jetbrains/jet/lang/resolve/calls/inference/TypeConstraintsImpl.java
@@ -0,0 +1,175 @@
+/*
+ * Copyright 2010-2012 JetBrains s.r.o.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.jetbrains.jet.lang.resolve.calls.inference;
+
+import com.google.common.collect.Lists;
+import com.google.common.collect.Sets;
+import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
+import org.jetbrains.jet.lang.descriptors.TypeParameterDescriptor;
+import org.jetbrains.jet.lang.types.CommonSupertypes;
+import org.jetbrains.jet.lang.types.JetType;
+import org.jetbrains.jet.lang.types.Variance;
+import org.jetbrains.jet.lang.types.checker.JetTypeChecker;
+
+import java.util.Collections;
+import java.util.Set;
+
+/**
+ * @author svtk
+ */
+public class TypeConstraintsImpl implements TypeConstraints {
+    private static final TypeConstraintsData EMPTY_CONSTRAINTS_DATA = new TypeConstraintsData(null, null, Collections.<JetType>emptySet());
+    private static class TypeConstraintsData {
+        private final JetType lowerConstraint;
+        private final JetType upperConstraint;
+        private final Set<JetType> conflicts;
+
+        private TypeConstraintsData(JetType lowerConstraint, JetType upperConstraint, Set<JetType> conflicts) {
+            this.lowerConstraint = lowerConstraint;
+            this.upperConstraint = upperConstraint;
+            this.conflicts = conflicts;
+        }
+
+        public JetType getLowerConstraint() {
+            return lowerConstraint;
+        }
+
+        public JetType getUpperConstraint() {
+            return upperConstraint;
+        }
+
+        public Set<JetType> getConflicts() {
+            return conflicts;
+        }
+    }
+
+    private final Variance variance;
+    private TypeConstraintsData typeConstraintsData = EMPTY_CONSTRAINTS_DATA;
+
+    private final Set<JetType> upperConstraints = Sets.newLinkedHashSet();
+    private final Set<JetType> lowerConstraints = Sets.newLinkedHashSet();
+    private final Set<JetType> equalConstraints = Sets.newLinkedHashSet();
+
+    private boolean changed = false;
+
+    public TypeConstraintsImpl(Variance variance) {
+        this.variance = variance;
+    }
+
+    @NotNull
+    @Override
+    public Variance getVariance() {
+        return variance;
+    }
+
+    public void addUpperConstraint(@NotNull JetType constraint) {
+        upperConstraints.add(constraint);
+        changed = true;
+    }
+
+    public void addLowerConstraint(@NotNull JetType constraint) {
+        lowerConstraints.add(constraint);
+        changed = true;
+    }
+
+    public void addEqualConstraint(@NotNull JetType constraint) {
+        equalConstraints.add(constraint);
+        changed = true;
+    }
+
+    private void updateResult() {
+        if (!changed) {
+            return;
+        }
+        JetType lowerConstraint = null;
+        JetType upperConstraint = null;
+        Set<JetType> conflicts = Sets.newLinkedHashSet();
+        if (!lowerConstraints.isEmpty()) {
+            lowerConstraint = CommonSupertypes.commonSupertype(lowerConstraints);
+        }
+        if (!upperConstraints.isEmpty()) {
+            //todo
+            upperConstraint = upperConstraints.iterator().next();
+        }
+
+        if (lowerConstraint != null && upperConstraint != null && !JetTypeChecker.INSTANCE.isSubtypeOf(lowerConstraint, upperConstraint)) {
+            conflicts.add(lowerConstraint);
+            conflicts.add(upperConstraint);
+        }
+
+        if (equalConstraints.size() > 1) {
+            conflicts.addAll(equalConstraints);
+        }
+        else if (equalConstraints.size() == 1) {
+            JetType value = equalConstraints.iterator().next();
+            if (lowerConstraint != null && !JetTypeChecker.INSTANCE.isSubtypeOf(lowerConstraint, value)) {
+                conflicts.add(lowerConstraint);
+                conflicts.add(value);
+            }
+            if (upperConstraint != null && !JetTypeChecker.INSTANCE.isSubtypeOf(value, upperConstraint)) {
+                conflicts.add(upperConstraint);
+                conflicts.add(value);
+            }
+            lowerConstraint = value;
+            upperConstraint = value;
+        }
+        typeConstraintsData = new TypeConstraintsData(lowerConstraint, upperConstraint, conflicts);
+    }
+
+    @Override
+    public boolean isSuccessful() {
+        updateResult();
+        return typeConstraintsData.getConflicts().isEmpty();
+    }
+
+    @Nullable
+    @Override
+    public JetType getLowerConstraint() {
+        updateResult();
+        return typeConstraintsData.getLowerConstraint();
+    }
+
+    @Nullable
+    @Override
+    public JetType getUpperConstraint() {
+        updateResult();
+        return typeConstraintsData.getUpperConstraint();
+    }
+
+    @NotNull
+    @Override
+    public Set<JetType> getConflicts() {
+        updateResult();
+        return typeConstraintsData.getConflicts();
+    }
+
+    @Override
+    public boolean isEmpty() {
+        updateResult();
+        return typeConstraintsData.getLowerConstraint() == null && typeConstraintsData.getUpperConstraint() == null && typeConstraintsData.getConflicts().isEmpty();
+    }
+
+    @Override
+    public String toString() {
+        return "TypeConstraints{" +
+               "upper=" + getUpperConstraint() +
+               ", lower=" + getLowerConstraint() +
+               ", conflicts=" + getConflicts() +
+               '}';
+    }
+}