NO Problem 1: (VAR v_NonEmpty:S X:S Y:S) (RULES 2nd(cons(X:S)) -> Y:S from(X:S) -> cons(X:S) ) Problem 1: Extra Variables Processor: -> Rules: 2nd(cons(X:S)) -> Y:S from(X:S) -> cons(X:S) -> The system has extra variables. The problem is infinite.