accumulation: fail on wrong engine

prism/src/prism/ProbModelChecker.java

@@ -485,6 +485,8 @@ public class ProbModelChecker extends NonProbModelChecker
 
 		if (useSimplePathAlgo) {
 			return checkProbPathFormulaSimple(expr, qual, statesOfInterest);
+		} else if (Expression.containsAccumulationExpression(expr)) {
+			throw new PrismException("Model checking of accumulation expressions not supported for this engine!");
 		} else {
 			return checkProbPathFormulaLTL(expr, qual, statesOfInterest);
 		}