MAYBE We are left with following problem, upon which TcT provides the certificate MAYBE. Strict Trs: { a__zeros() -> cons(0(), zeros()) , a__zeros() -> zeros() , a__and(X1, X2) -> and(X1, X2) , a__and(tt(), X) -> mark(X) , mark(cons(X1, X2)) -> cons(mark(X1), X2) , mark(0()) -> 0() , mark(zeros()) -> a__zeros() , mark(tt()) -> tt() , mark(nil()) -> nil() , mark(s(X)) -> s(mark(X)) , mark(and(X1, X2)) -> a__and(mark(X1), X2) , mark(length(X)) -> a__length(mark(X)) , a__length(X) -> length(X) , a__length(cons(N, L)) -> s(a__length(mark(L))) , a__length(nil()) -> 0() } Obligation: innermost runtime complexity Answer: MAYBE The input cannot be shown compatible Arrrr..