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diff --git a/bundles/org.simantics.utils.datastructures/src/org/simantics/utils/datastructures/collections/LightweightList.java b/bundles/org.simantics.utils.datastructures/src/org/simantics/utils/datastructures/collections/LightweightList.java
new file mode 100644
index 000000000..2572fcf8e
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+++ b/bundles/org.simantics.utils.datastructures/src/org/simantics/utils/datastructures/collections/LightweightList.java
@@ -0,0 +1,245 @@
+/*******************************************************************************
+ * 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.collections;
+
+import java.util.Arrays;
+
+
+public class LightweightList {
+
+	public static final Object EMPTY = new LL0();
+	
+	public static Object add(Object list, Object value) {
+		if(list instanceof LL)
+			return ((LL)list).add(value);
+		else
+			return new LL2(list, value);
+	}
+	
+	public static Object remove(Object list, Object value) {
+		if(list instanceof LL)
+			return ((LL)list).remove(value);
+		else
+			return value.equals(list) ? EMPTY : list;
+	}
+
+	public static int size(Object list) {
+		if(list instanceof LL)
+			return ((LL)list).size();
+		else
+			return 1;
+	}
+	
+	public static boolean isEmpty(Object list) {
+		return list==EMPTY;
+	}	 
+	
+	public static Object[] toArray(Object list) {
+		if(list == null)
+			return EMPTY_ARRAY;
+		else if(list instanceof LL)
+			return ((LL)list).toArray();
+		else
+			return new Object[] { list };
+	}
+	
+	public static interface IProcedure {
+		void exec(Object obj);
+	}
+	
+	public static void forEach(Object list, IProcedure proc) {
+		if(list == null)
+			return;
+		else if(list instanceof LL)
+			((LL)list).forEach(proc);
+		else
+			proc.exec(list);
+	}
+	
+	private static interface LL {
+		Object add(Object value);
+		Object remove(Object value);
+		int size();
+		Object[] toArray();
+		void forEach(IProcedure proc);
+	}
+	
+	static final Object[] EMPTY_ARRAY = new Object[0];
+	private static class LL0 implements LL {		
+
+		@Override
+		public Object add(Object value) {
+			return value;
+		}
+
+		@Override
+		public Object remove(Object value) {
+			return this;
+		}
+
+		@Override
+		public int size() {
+			return 0;
+		}
+
+		@Override
+		public Object[] toArray() {
+			return EMPTY_ARRAY;
+		}
+
+		@Override
+		public void forEach(IProcedure proc) {
+		}
+		
+	}
+	
+	private static class LL2 implements LL {
+
+		Object v0, v1;		
+		
+		public LL2(Object v0, Object v1) {
+			this.v0 = v0;
+			this.v1 = v1;
+		}
+
+		@Override
+		public Object add(Object value) {
+			return new LL3(v0, v1, value);
+		}
+
+		@Override
+		public Object remove(Object value) {
+			if(value.equals(v0))
+				return v1;
+			else if(value.equals(v1))
+				return v0;
+			else
+				return this;
+		}
+
+		@Override
+		public int size() {
+			return 2;
+		}
+
+		@Override
+		public Object[] toArray() {
+			return new Object[] { v0, v1 };
+		}
+
+		@Override
+		public void forEach(IProcedure proc) {
+			proc.exec(v0);
+			proc.exec(v1);
+		}
+		
+	}
+	
+	private static class LL3 implements LL {
+
+		Object v0, v1, v2;		
+		
+		public LL3(Object v0, Object v1, Object v2) {
+			this.v0 = v0;
+			this.v1 = v1;
+			this.v2 = v2;
+		}
+
+		@Override
+		public Object add(Object value) {
+			return new LLN(v0, v1, v2, value);
+		}
+
+		@Override
+		public Object remove(Object value) {
+			if(value.equals(v0))
+				return new LL2(v1, v2);
+			else if(value.equals(v1))
+				return new LL2(v0, v2);
+			else if(value.equals(v2))
+				return new LL2(v0, v1);
+			else
+				return this;
+		}
+
+		@Override
+		public int size() {
+			return 3;
+		}
+		
+		@Override
+		public Object[] toArray() {
+			return new Object[] { v0, v1, v2 };
+		}
+		
+		@Override
+		public void forEach(IProcedure proc) {
+			proc.exec(v0);
+			proc.exec(v1);
+			proc.exec(v2);
+		}
+	}
+	
+	private static class LLN implements LL {
+
+		Object[] array;
+		int size;
+		
+		public LLN(Object v0, Object v1, Object v2, Object v3) {
+			array = new Object[] { v0, v1, v2, v3, null, null };
+			size = 4;
+		}
+
+		@Override
+		public Object add(Object value) {
+			if(size==array.length)
+				array = Arrays.copyOf(array, (size*3)/2+1);			
+			array[size++] = value;
+			return this;
+		}
+
+		@Override
+		public Object remove(Object value) {
+			for(int i=0;i<size;++i) {
+				if(value.equals(array[i])) {
+					while(i < size-1) { 
+						array[i] = array[i+1];
+						++i;
+					}
+					array[--size] = null;
+					if(size == 3)
+						return new LL3(array[0], array[1], array[2]);
+					else
+						return this;
+				}
+			}
+			return this;			
+		}
+
+		@Override
+		public int size() {
+			return size;
+		}
+		
+		@Override
+		public Object[] toArray() {
+			return Arrays.copyOf(array, size);
+		}
+		
+		@Override
+		public void forEach(IProcedure proc) {
+			for(int i=0;i<size;++i)
+				proc.exec(array[i]);
+		}
+	}	
+	
+}