MAYBE We are left with following problem, upon which TcT provides the certificate MAYBE. Strict Trs: { a__from(X) -> cons(mark(X), from(s(X))) , a__from(X) -> from(X) , mark(cons(X1, X2)) -> cons(mark(X1), X2) , mark(from(X)) -> a__from(mark(X)) , mark(s(X)) -> s(mark(X)) , mark(0()) -> 0() , mark(nil()) -> nil() , mark(take(X1, X2)) -> a__take(mark(X1), mark(X2)) , mark(head(X)) -> a__head(mark(X)) , mark(2nd(X)) -> a__2nd(mark(X)) , mark(sel(X1, X2)) -> a__sel(mark(X1), mark(X2)) , a__head(X) -> head(X) , a__head(cons(X, XS)) -> mark(X) , a__2nd(X) -> 2nd(X) , a__2nd(cons(X, XS)) -> a__head(mark(XS)) , a__take(X1, X2) -> take(X1, X2) , a__take(s(N), cons(X, XS)) -> cons(mark(X), take(N, XS)) , a__take(0(), XS) -> nil() , a__sel(X1, X2) -> sel(X1, X2) , a__sel(s(N), cons(X, XS)) -> a__sel(mark(N), mark(XS)) , a__sel(0(), cons(X, XS)) -> mark(X) } Obligation: innermost runtime complexity Answer: MAYBE The input cannot be shown compatible Arrrr..