diff --git a/prism/src/explicit/ModelExpressionTransformation.java b/prism/src/explicit/ModelExpressionTransformation.java
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+//==============================================================================
+//	
+//	Copyright (c) 2015-
+//	Authors:
+//	* Joachim Klein <klein@tcs.inf.tu-dresden.de> (TU Dresden)
+//	
+//------------------------------------------------------------------------------
+//	
+//	This file is part of PRISM.
+//	
+//	PRISM is free software; you can redistribute it and/or modify
+//	it under the terms of the GNU General Public License as published by
+//	the Free Software Foundation; either version 2 of the License, or
+//	(at your option) any later version.
+//	
+//	PRISM is distributed in the hope that it will be useful,
+//	but WITHOUT ANY WARRANTY; without even the implied warranty of
+//	MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+//	GNU General Public License for more details.
+//	
+//	You should have received a copy of the GNU General Public License
+//	along with PRISM; if not, write to the Free Software Foundation,
+//	Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
+//	
+//==============================================================================
+
+package explicit;
+
+import parser.ast.Expression;
+
+/**
+ * Interface for a model and expression transformation.<br>
+ *
+ * Implementing classes provide a combined model and expression transformation, allowing the calculation
+ * of a (potentially simpler) expression in the transformed model to calculate the result of the
+ * original expression in the original model.<br>
+ *
+ * The general idea is the following sequence of calls:<br>
+ *
+ * {@code ModelExpressionTransformation t = ...;}<br>
+ * {@code StateValues resultTransformed = check t.getTransformedExpression() in t.getTransformedModel()}<br>
+ * {@code StateValues result = t.projectToOriginalModel(resultTransformed);}
+ */
+public interface ModelExpressionTransformation<OriginalModel extends Model, TransformedModel extends Model>
+       extends ModelTransformation<OriginalModel, TransformedModel> {
+
+	/** Get the original expression. */
+	public Expression getOriginalExpression();
+
+	/** Get the transformed expression. */
+	public Expression getTransformedExpression();
+}