Small fix in OpRelOpBound toString method.

git-svn-id: https://www.prismmodelchecker.org/svn/prism/prism/trunk@11403 bbc10eb1-c90d-0410-af57-cb519fbb1720

prism/src/prism/OpRelOpBound.java

@@ -122,6 +122,6 @@ public class OpRelOpBound
 	@Override
 	public String toString()
 	{
-		return op + relOp.toString() + bound;
+		return op + relOp.toString() + (isNumeric() ? "?" : bound);
 	}
 }