MAYBE We are left with following problem, upon which TcT provides the certificate MAYBE. Strict Trs: { and(false(), false()) -> false() , and(false(), true()) -> false() , and(true(), false()) -> false() , and(true(), true()) -> true() , eq(nil(), nil()) -> true() , eq(nil(), cons(T, L)) -> false() , eq(cons(T, L), nil()) -> false() , eq(cons(T, L), cons(Tp, Lp)) -> and(eq(T, Tp), eq(L, Lp)) , eq(var(L), var(Lp)) -> eq(L, Lp) , eq(var(L), apply(T, S)) -> false() , eq(var(L), lambda(X, T)) -> false() , eq(apply(T, S), var(L)) -> false() , eq(apply(T, S), apply(Tp, Sp)) -> and(eq(T, Tp), eq(S, Sp)) , eq(apply(T, S), lambda(X, Tp)) -> false() , eq(lambda(X, T), var(L)) -> false() , eq(lambda(X, T), apply(Tp, Sp)) -> false() , eq(lambda(X, T), lambda(Xp, Tp)) -> and(eq(T, Tp), eq(X, Xp)) , if(false(), var(K), var(L)) -> var(L) , if(true(), var(K), var(L)) -> var(K) , ren(X, Y, apply(T, S)) -> apply(ren(X, Y, T), ren(X, Y, S)) , ren(X, Y, lambda(Z, T)) -> lambda(var(cons(X, cons(Y, cons(lambda(Z, T), nil())))), ren(X, Y, ren(Z, var(cons(X, cons(Y, cons(lambda(Z, T), nil())))), T))) , ren(var(L), var(K), var(Lp)) -> if(eq(L, Lp), var(K), var(Lp)) } Obligation: innermost runtime complexity Answer: MAYBE The input cannot be shown compatible Arrrr..