Use Expression instead of plain strings for counterexamples

libsmtutil/CHCSolverInterface.h

@@ -44,9 +44,7 @@ public:
 	/// Needs to bound all vars as universally quantified.
 	virtual void addRule(Expression const& _expr, std::string const& _name) = 0;
 
-	/// first: predicate name
-	/// second: predicate arguments
-	using CexNode = std::pair<std::string, std::vector<std::string>>;
+	using CexNode = Expression;
 	struct CexGraph
 	{
 		std::map<unsigned, CexNode> nodes;