YES(?,ELEMENTARY) We are left with following problem, upon which TcT provides the certificate YES(?,ELEMENTARY). Strict Trs: { bin(x, 0()) -> s(0()) , bin(0(), s(y)) -> 0() , bin(s(x), s(y)) -> +(bin(x, s(y)), bin(x, y)) } Obligation: innermost runtime complexity Answer: YES(?,ELEMENTARY) The input was oriented with the instance of 'Lightweight Multiset Path Order' as induced by the safe mapping safe(bin) = {2}, safe(0) = {}, safe(s) = {1}, safe(+) = {1, 2} and precedence empty . Following symbols are considered recursive: {bin} The recursion depth is 1. For your convenience, here are the satisfied ordering constraints: bin(x; 0()) > s(; 0()) bin(0(); s(; y)) > 0() bin(s(; x); s(; y)) > +(; bin(x; s(; y)), bin(x; y)) Hurray, we answered YES(?,ELEMENTARY)