diff --git a/prism/src/parser/ast/Expression.java b/prism/src/parser/ast/Expression.java
index c0ecb67e..358b860c 100644
--- a/prism/src/parser/ast/Expression.java
+++ b/prism/src/parser/ast/Expression.java
@@ -847,6 +847,18 @@ public abstract class Expression extends ASTElement
 		return false;
 	}
 
+	/**
+	 * Test if an expression is either an ExpressionHOA or a negated ExpressionHOA.
+	 */
+	public static boolean isHOA(Expression expr) {
+		if (expr instanceof ExpressionHOA) return true;
+		if ( (isNot(expr) || isParenth(expr)) &&
+		     isHOA(((ExpressionUnaryOp)expr).getOperand())) {
+			return true;
+		}
+		return false;
+	}
+
 	/**
 	 * Test if an expression contains time bounds on temporal operators 
 	 */
diff --git a/prism/src/parser/ast/ExpressionHOA.java b/prism/src/parser/ast/ExpressionHOA.java
new file mode 100644
index 00000000..684612dd
--- /dev/null
+++ b/prism/src/parser/ast/ExpressionHOA.java
@@ -0,0 +1,186 @@
+//==============================================================================
+//	
+//	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 parser.ast;
+
+import parser.EvaluateContext;
+import parser.type.TypePathBool;
+import parser.visitor.ASTVisitor;
+import prism.PrismLangException;
+import prism.Pair;
+
+import java.util.ArrayList;
+import java.util.List;
+
+import param.BigRational;
+
+/**
+ * An path expression where the set of paths is determined by
+ * a HOA automaton, stored in a file.
+ *
+ * An optional list of renames allows for atomic propositions in
+ * the automaton to be associated with sets of states satisfying an expression
+ * in the model. Non-renamed atomic propositions are treated as labels in the model.
+ */
+public class ExpressionHOA extends Expression
+{
+	/** The automaton file name */
+	private QuotedString automatonFile;
+
+	/**
+	 * A list of (AP, expression) pairs, relating atomic propositions
+	 * in the automaton with expressions in the model.
+	 */
+	private List<Pair<String, Expression>> apRenames;
+
+	/** Constructor. */
+	public ExpressionHOA(QuotedString automatonFile)
+	{
+		this.automatonFile = automatonFile;
+		apRenames = new ArrayList<Pair<String, Expression>>();
+		setType(TypePathBool.getInstance());
+	}
+
+	@Override
+	public boolean isConstant()
+	{
+		return false;
+	}
+
+	@Override
+	public boolean isProposition()
+	{
+		return false;
+	}
+
+	@Override
+	public Object evaluate(EvaluateContext ec) throws PrismLangException
+	{
+		throw new PrismLangException("Cannot evaluate a HOA path operator without a path");
+	}
+
+	@Override
+	public BigRational evaluateExact(EvaluateContext ec) throws PrismLangException
+	{
+		throw new PrismLangException("Cannot evaluate a HOA path operator without a path");
+	}
+
+	@Override
+	public boolean returnsSingleValue()
+	{
+		return false;
+	}
+
+	@Override
+	public Expression deepCopy()
+	{
+		ExpressionHOA result = new ExpressionHOA(automatonFile);
+		for (Pair<String, Expression> rename : getRenames()) {
+			result.addRename(rename.getKey(), rename.getValue().deepCopy());
+		}
+		return result;
+	}
+
+	@Override
+	public Object accept(ASTVisitor v) throws PrismLangException
+	{
+		return v.visit(this);
+	}
+
+	@Override
+	public String toString()
+	{
+		StringBuilder sb = new StringBuilder();
+		sb.append("HOA: { ");
+		sb.append(automatonFile != null ? automatonFile : "");
+		for (Pair<String, Expression> rename : apRenames) {
+			sb.append(", \"");
+			sb.append(rename.getKey());
+			sb.append("\" <- ");
+			sb.append(rename.getValue());
+		}
+		sb.append(" }");
+		return sb.toString();
+	}
+
+	/** Get the automaton filename. */
+	public QuotedString getAutomatonFile()
+	{
+		return automatonFile;
+	}
+
+	/** Set the automaton filename. */
+	public void setAutomatonFile(QuotedString automatonFile)
+	{
+		this.automatonFile = automatonFile;
+	}
+
+	/** Add a rename from an atomic proposition to an expression in the model */
+	public void addRename(String ap, Expression expression)
+	{
+		apRenames.add(new Pair<String, Expression>(ap, expression));
+	}
+
+	/** Get the list of renames */
+	public List<Pair<String, Expression>> getRenames()
+	{
+		return apRenames;
+	}
+
+	@Override
+	public int hashCode()
+	{
+		final int prime = 31;
+		int result = 1;
+		result = prime * result + ((automatonFile == null) ? 0 : automatonFile.hashCode());
+		result = prime * result + ((apRenames == null) ? 0 : apRenames.hashCode());
+		return result;
+	}
+
+	@Override
+	public boolean equals(Object obj)
+	{
+		if (this == obj)
+			return true;
+		if (obj == null)
+			return false;
+		if (!(obj instanceof ExpressionHOA))
+			return false;
+		ExpressionHOA other = (ExpressionHOA) obj;
+		if (automatonFile == null) {
+			if (other.automatonFile != null)
+				return false;
+		} else if (!automatonFile.equals(other.automatonFile))
+			return false;
+		if (apRenames == null) {
+			if (other.apRenames != null)
+				return false;
+		} else if (!apRenames.equals(other.apRenames))
+			return false;
+		return true;
+	}
+
+}
diff --git a/prism/src/parser/visitor/ASTTraverse.java b/prism/src/parser/visitor/ASTTraverse.java
index c27744d0..e2de1872 100644
--- a/prism/src/parser/visitor/ASTTraverse.java
+++ b/prism/src/parser/visitor/ASTTraverse.java
@@ -27,6 +27,7 @@
 package parser.visitor;
 
 import parser.ast.*;
+import prism.Pair;
 import prism.PrismLangException;
 
 // Performs a depth-first traversal of an asbtract syntax tree (AST).
@@ -633,6 +634,18 @@ public class ASTTraverse implements ASTVisitor
 	}
 	public void visitPost(ExpressionFilter e) throws PrismLangException { defaultVisitPost(e); }
 	// -----------------------------------------------------------------------------------
+	public void visitPre(ExpressionHOA e) throws PrismLangException { defaultVisitPre(e); }
+	public Object visit(ExpressionHOA e) throws PrismLangException
+	{
+		visitPre(e);
+		if (e.getAutomatonFile() != null) e.getAutomatonFile().accept(this);
+		for (Pair<String, Expression> rename : e.getRenames())
+			rename.getValue().accept(this);
+		visitPost(e);
+		return null;
+	}
+	public void visitPost(ExpressionHOA e) throws PrismLangException { defaultVisitPost(e); }
+	// -----------------------------------------------------------------------------------
 	public void visitPre(Filter e) throws PrismLangException { defaultVisitPre(e); }
 	public Object visit(Filter e) throws PrismLangException
 	{
diff --git a/prism/src/parser/visitor/ASTTraverseModify.java b/prism/src/parser/visitor/ASTTraverseModify.java
index 0fb53ae9..3d9024da 100644
--- a/prism/src/parser/visitor/ASTTraverseModify.java
+++ b/prism/src/parser/visitor/ASTTraverseModify.java
@@ -27,6 +27,7 @@
 package parser.visitor;
 
 import parser.ast.*;
+import prism.Pair;
 import prism.PrismLangException;
 
 // Variant of ASTTraverse.
@@ -647,6 +648,18 @@ public class ASTTraverseModify implements ASTVisitor
 	}
 	public void visitPost(ExpressionFilter e) throws PrismLangException { defaultVisitPost(e); }
 	// -----------------------------------------------------------------------------------
+	public void visitPre(ExpressionHOA e) throws PrismLangException { defaultVisitPre(e); }
+	public Object visit(ExpressionHOA e) throws PrismLangException
+	{
+		visitPre(e);
+		if (e.getAutomatonFile() != null) e.setAutomatonFile((QuotedString) e.getAutomatonFile().accept(this));
+		for (Pair<String, Expression> rename : e.getRenames())
+			rename.setValue((Expression) rename.getValue().accept(this));
+		visitPost(e);
+		return e;
+	}
+	public void visitPost(ExpressionHOA e) throws PrismLangException { defaultVisitPost(e); }
+	// -----------------------------------------------------------------------------------
 	public void visitPre(ForLoop e) throws PrismLangException { defaultVisitPre(e); }
 	public Object visit(ForLoop e) throws PrismLangException
 	{
diff --git a/prism/src/parser/visitor/ASTVisitor.java b/prism/src/parser/visitor/ASTVisitor.java
index 4adc6794..5002f7ee 100644
--- a/prism/src/parser/visitor/ASTVisitor.java
+++ b/prism/src/parser/visitor/ASTVisitor.java
@@ -85,6 +85,7 @@ public interface ASTVisitor
 	public Object visit(ExpressionObs e) throws PrismLangException;
 	public Object visit(ExpressionProp e) throws PrismLangException;
 	public Object visit(ExpressionFilter e) throws PrismLangException;
+	public Object visit(ExpressionHOA e) throws PrismLangException;
 	// ASTElement classes (misc.)
 	public Object visit(Filter e) throws PrismLangException;
 	public Object visit(ForLoop e) throws PrismLangException;