MAYBE We are left with following problem, upon which TcT provides the certificate MAYBE. Strict Trs: { last(nil()) -> 0() , last(cons(x, nil())) -> x , last(cons(x, cons(y, xs))) -> last(cons(y, xs)) , del(x, nil()) -> nil() , del(x, cons(y, xs)) -> if(eq(x, y), x, y, xs) , if(true(), x, y, xs) -> xs , if(false(), x, y, xs) -> cons(y, del(x, xs)) , eq(0(), 0()) -> true() , eq(0(), s(y)) -> false() , eq(s(x), 0()) -> false() , eq(s(x), s(y)) -> eq(x, y) , reverse(nil()) -> nil() , reverse(cons(x, xs)) -> cons(last(cons(x, xs)), reverse(del(last(cons(x, xs)), cons(x, xs)))) } Obligation: innermost runtime complexity Answer: MAYBE The input cannot be shown compatible Arrrr..