YES(?,POLY) We are left with following problem, upon which TcT provides the certificate YES(?,POLY). Strict Trs: { filter(cons(X), 0(), M) -> cons(0()) , filter(cons(X), s(N), M) -> cons(X) , sieve(cons(0())) -> cons(0()) , sieve(cons(s(N))) -> cons(s(N)) , nats(N) -> cons(N) , zprimes() -> sieve(nats(s(s(0())))) } Obligation: innermost runtime complexity Answer: YES(?,POLY) The input was oriented with the instance of 'Polynomial Path Order' as induced by the safe mapping safe(filter) = {2, 3}, safe(cons) = {1}, safe(0) = {}, safe(s) = {1}, safe(sieve) = {1}, safe(nats) = {1}, safe(zprimes) = {} and precedence filter > sieve, filter > nats, nats > sieve, zprimes > sieve, zprimes > nats, filter ~ zprimes . Following symbols are considered recursive: {} The recursion depth is 0. For your convenience, here are the satisfied ordering constraints: filter(cons(; X); 0(), M) > cons(; 0()) filter(cons(; X); s(; N), M) > cons(; X) sieve(; cons(; 0())) > cons(; 0()) sieve(; cons(; s(; N))) > cons(; s(; N)) nats(; N) > cons(; N) zprimes() > sieve(; nats(; s(; s(; 0())))) Hurray, we answered YES(?,POLY)