YES(?,PRIMREC) We are left with following problem, upon which TcT provides the certificate YES(?,PRIMREC). Strict Trs: { f(0()) -> 0() , f(s(0())) -> s(0()) , f(s(s(x))) -> p(h(g(x))) , f(s(s(x))) -> +(p(g(x)), q(g(x))) , p(pair(x, y)) -> x , h(x) -> pair(+(p(x), q(x)), p(x)) , g(0()) -> pair(s(0()), s(0())) , g(s(x)) -> h(g(x)) , g(s(x)) -> pair(+(p(g(x)), q(g(x))), p(g(x))) , +(x, 0()) -> x , +(x, s(y)) -> s(+(x, y)) , q(pair(x, y)) -> y } Obligation: innermost runtime complexity Answer: YES(?,PRIMREC) The input was oriented with the instance of'multiset path order' as induced by the precedence f > s, f > p, f > h, f > g, f > pair, f > +, f > q, 0 > f, 0 > s, 0 > p, 0 > h, 0 > g, 0 > pair, 0 > +, 0 > q, h > s, h > p, h > pair, h > +, h > q, g > s, g > p, g > h, g > pair, g > +, g > q, pair > s, pair > p, pair > q, + > s, + > p, + > pair, + > q, p ~ q . Hurray, we answered YES(?,PRIMREC)