diff --git a/prism/src/explicit/ProductState.java b/prism/src/explicit/ProductState.java
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+++ b/prism/src/explicit/ProductState.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;
+
+/**
+ * A product state, i.e., a pair of two indizes for
+ * referencing the states of the left and right part of the product.
+ * <br>
+ * Objects are {@code Comparable}, i.e., can be used in TreeSets etc.
+ */
+public class ProductState implements Comparable<ProductState>
+{
+	/** The first state */
+	private Integer state_1;
+	/** The second state */
+	private Integer state_2;
+
+	/** Constructor */
+	public ProductState(Integer state_1, Integer state_2)
+	{
+		this.state_1 = state_1;
+		this.state_2 = state_2;
+	}
+
+	/** Get the first state */
+	public Integer getFirstState()
+	{
+		return state_1;
+	}
+
+	/** Get the second state */
+	public Integer getSecondState()
+	{
+		return state_2;
+	}
+
+	@Override
+	public String toString()
+	{
+		return "[" + state_1 + "," + state_2 + "]";
+	}
+
+	@Override
+	public int compareTo(ProductState other)
+	{
+		int rv = state_1.compareTo(state_2);
+		if (rv == 0) {
+			return state_2.compareTo(other.state_2);
+		} else {
+			return rv;
+		}
+	}
+
+	@Override
+	public int hashCode()
+	{
+		final int prime = 31;
+		int result = 1;
+		result = prime * result + ((state_1 == null) ? 0 : state_1.hashCode());
+		result = prime * result + ((state_2 == null) ? 0 : state_2.hashCode());
+		return result;
+	}
+
+	@Override
+	public boolean equals(Object obj)
+	{
+		if (this == obj)
+			return true;
+		if (obj == null)
+			return false;
+		if (getClass() != obj.getClass())
+			return false;
+		ProductState other = (ProductState) obj;
+		return state_1.equals(other.state_1) &&
+				state_2.equals(other.state_2);
+	}
+}