diff --git a/AlgebraicDataflowArchitectureModel/src/models/dataConstraintModel/DataConstraintModel.java b/AlgebraicDataflowArchitectureModel/src/models/dataConstraintModel/DataConstraintModel.java
index 79f8fe0..3686bb8 100644
--- a/AlgebraicDataflowArchitectureModel/src/models/dataConstraintModel/DataConstraintModel.java
+++ b/AlgebraicDataflowArchitectureModel/src/models/dataConstraintModel/DataConstraintModel.java
@@ -122,7 +122,24 @@
 	public static final Symbol left = new Symbol("left", 1, Symbol.Type.PREFIX, "getLeft", Symbol.Type.METHOD);
 	public static final Symbol right = new Symbol("right", 1, Symbol.Type.PREFIX, "getRight", Symbol.Type.METHOD);
 	public static final Symbol insert = new Symbol("insert", 3, Symbol.Type.PREFIX, "put", Symbol.Type.METHOD_WITH_SIDE_EFFECT);
-	public static final Symbol lookup = new Symbol("lookup", 2, Symbol.Type.PREFIX, "get", Symbol.Type.METHOD);
+//	public static final Symbol lookup = new Symbol("lookup", 2, Symbol.Type.PREFIX, "get", Symbol.Type.METHOD);
+	public static final Symbol lookup = new Symbol("lookup", 2, Symbol.Type.PREFIX, new Symbol.IImplGenerator() {
+		final int count[] = {0};
+		@Override
+		public String generate(Type type, String[] childrenImpl, String[] childrenSideEffects, String[] sideEffect) {
+			String temp = "temp_get" + count[0];
+			String impl = childrenSideEffects[0] + childrenSideEffects[1];
+			impl += type.getInterfaceTypeName() + " " + temp + ";\n";
+			impl += "if (" + childrenImpl[0] + ".get(" + childrenImpl[1] + ") != null) {\n";
+			impl += "\t" + temp + " = " + childrenImpl[0] + ".get(" + childrenImpl[1] + ");\n";
+			impl += "} else {\n";
+			impl += "\t" + temp + " = " + getDefaultValue(type) + ";\n";
+			impl += "}\n";
+			sideEffect[0] = impl;
+			count[0]++;
+			return temp;
+		}
+	});
 		
 	static {
 		add.setInverses(new Symbol[] {sub, sub});
@@ -306,6 +323,23 @@
 	public static boolean isListType(Type type) {
 		return typeList.isAncestorOf(type);
 	}
+
+	public static String getDefaultValue(Type type) {
+		if (type == typeInt) {
+			return "0";
+		} else if (type == typeLong) {
+			return "0L";
+		} else if (type == typeFloat) {
+			return "0.0f";
+		} else if (type == typeDouble) {
+			return "0.0";
+		} else if (type == typeBoolean) {
+			return "false";
+		} else if (type == typeString) {
+			return "\"\"";
+		}
+		return "new " + type.getImplementationTypeName() + "()";
+	}
 	
 	@Override
 	public String toString() {