@@ -136,7 +136,7 @@ usable simpl True n ns
136136 case lookup n ls of
137137 Just 0 -> return (False, ns)
138138 Just i -> return (True, ns)
139− _ -> return (True, ns)
139+ _ -> return (False, ns)
140140usable simpl False n ns
141141 = case lookup n ns of
142142 Just 0 -> return (False, ns)