YES(?,PRIMREC) We are left with following problem, upon which TcT provides the certificate YES(?,PRIMREC). Strict Trs: { not(true()) -> false() , not(false()) -> true() , odd(0()) -> false() , odd(s(x)) -> not(odd(x)) , +(x, 0()) -> x , +(x, s(y)) -> s(+(x, y)) , +(s(x), y) -> s(+(x, y)) } Obligation: innermost runtime complexity Answer: YES(?,PRIMREC) The input was oriented with the instance of'multiset path order' as induced by the precedence not > true, not > false, odd > not, odd > true, odd > false, 0 > not, 0 > true, 0 > false, 0 > odd, 0 > s, s > not, s > true, s > false, + > not, + > true, + > false, + > odd, + > s, 0 ~ + . Hurray, we answered YES(?,PRIMREC)