YES(?,O(n^1)) We are left with following problem, upon which TcT provides the certificate YES(?,O(n^1)). Strict Trs: { admit(x, nil()) -> nil() , admit(x, .(u, .(v, .(w(), z)))) -> cond(=(sum(x, u, v), w()), .(u, .(v, .(w(), admit(carry(x, u, v), z))))) , cond(true(), y) -> y } Obligation: innermost runtime complexity Answer: YES(?,O(n^1)) The input was oriented with the instance of 'Small Polynomial Path Order (PS,1-bounded)' as induced by the safe mapping safe(admit) = {1}, safe(nil) = {}, safe(.) = {1, 2}, safe(w) = {}, safe(cond) = {1, 2}, safe(=) = {1, 2}, safe(sum) = {1, 2, 3}, safe(carry) = {1, 2, 3}, safe(true) = {} and precedence admit > cond . Following symbols are considered recursive: {admit} The recursion depth is 1. For your convenience, here are the satisfied ordering constraints: admit(nil(); x) > nil() admit(.(; u, .(; v, .(; w(), z))); x) > cond(; =(; sum(; x, u, v), w()), .(; u, .(; v, .(; w(), admit(z; carry(; x, u, v)))))) cond(; true(), y) > y Hurray, we answered YES(?,O(n^1))