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diff --git a/bundles/org.simantics.utils.datastructures/src/org/simantics/utils/datastructures/Max2Collection.java b/bundles/org.simantics.utils.datastructures/src/org/simantics/utils/datastructures/Max2Collection.java
new file mode 100644
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+++ b/bundles/org.simantics.utils.datastructures/src/org/simantics/utils/datastructures/Max2Collection.java
@@ -0,0 +1,175 @@
+/*******************************************************************************
+ * Copyright (c) 2007, 2010 Association for Decentralized Information Management
+ * in Industry THTH ry.
+ * All rights reserved. This program and the accompanying materials
+ * are made available under the terms of the Eclipse Public License v1.0
+ * which accompanies this distribution, and is available at
+ * http://www.eclipse.org/legal/epl-v10.html
+ *
+ * Contributors:
+ *     VTT Technical Research Centre of Finland - initial API and implementation
+ *******************************************************************************/
+package org.simantics.utils.datastructures;
+
+import java.util.Collection;
+import java.util.Iterator;
+
+/**
+ * Collection with at most 2 elements. Does not use equals for comparison.
+ */
+public class Max2Collection<T> implements Collection<T> {
+
+    public T first;
+    public T second;    
+    
+    static class CollectionIsFullException extends RuntimeException {
+
+        private static final long serialVersionUID = 8693601196559590064L;
+        
+    }        
+    
+    public Max2Collection() {        
+    }
+            
+    public Max2Collection(T first, T second) {
+        this.first = first;
+        this.second = second;
+    }
+
+    public Max2Collection(T first) {
+        this.first = first;
+    }
+
+    final public T get(int i) {
+        if(i==0)
+            return first;
+        else if(i==1)
+            return second;
+        else
+            throw new IndexOutOfBoundsException();
+    }
+    
+    final public T getOther(T el) {
+        if(first != el)
+            return first;
+        else
+            return second;        
+    }
+    
+    final public boolean add(T el) {
+        if(first == null)
+            first = el;
+        else if(second == null)
+            second = el;
+        else
+            throw new CollectionIsFullException();
+        return true;
+    }
+    
+    final public boolean remove(Object el) {
+        if(first == el) {
+            first = second;
+            second = null;
+            return true;
+        }
+        else if(second == el) {
+            second = null;
+            return true;
+        }
+        else
+            return false;        
+    }
+    
+    final public void setFirstElement(T el) {
+        if(second == el) {
+            second = first;
+            first = el;
+        }               
+    }
+    
+    final public void setSecondElement(T el) {
+        if(first == el) {
+            first = second;
+            second = el;
+        }
+                
+    }
+    
+    final public int size() {
+        if(first == null)
+            return 0;
+        else if(second == null)
+            return 1;
+        else
+            return 2;
+    }
+    
+    final public boolean isEmpty() {
+        return first == null;
+    }
+    
+    final public boolean isFull() {
+        return second != null;
+    }
+
+    @Override
+    public boolean addAll(Collection<? extends T> c) {        
+        for(T o : c)
+            add(o);
+        return !c.isEmpty();
+    }
+
+    @Override
+    public void clear() {
+        first = null;
+        second = null; // necessary for gc
+    }
+
+    @Override
+    public boolean contains(Object o) {
+        return first == o || second == o;
+    }
+
+    @Override
+    public boolean containsAll(Collection<?> c) {
+        for(Object o : c)
+            if(!contains(o))
+                return false;
+        return true;
+    }
+
+    @Override
+    public Iterator<T> iterator() {
+        throw new UnsupportedOperationException();
+    }
+
+    @Override
+    public boolean removeAll(Collection<?> c) {
+        boolean removed = false;
+        for(Object o : c)
+            removed |= remove(o);
+        return removed;
+    }
+
+    @Override
+    public boolean retainAll(Collection<?> c) {
+        throw new UnsupportedOperationException();
+    }
+
+    @Override
+    public Object[] toArray() {
+        if(first == null)
+            return new Object[0];
+        if(second == null)
+            return new Object[] {first};
+        else
+            return new Object[] {first, second};        
+    }
+
+    @SuppressWarnings("hiding")
+    @Override
+    public <T> T[] toArray(T[] a) {       
+        throw new UnsupportedOperationException();
+    }
+    
+}