YES(?,O(1)) We are left with following problem, upon which TcT provides the certificate YES(?,O(1)). Strict Trs: { 2nd(cons(X, n__cons(Y, Z))) -> activate(Y) , cons(X1, X2) -> n__cons(X1, X2) , activate(X) -> X , activate(n__cons(X1, X2)) -> cons(X1, X2) , activate(n__from(X)) -> from(X) , from(X) -> cons(X, n__from(s(X))) , from(X) -> n__from(X) } Obligation: innermost runtime complexity Answer: YES(?,O(1)) Arguments of following rules are not normal-forms: { 2nd(cons(X, n__cons(Y, Z))) -> activate(Y) } All above mentioned rules can be savely removed. We are left with following problem, upon which TcT provides the certificate YES(?,O(1)). Strict Trs: { cons(X1, X2) -> n__cons(X1, X2) , activate(X) -> X , activate(n__cons(X1, X2)) -> cons(X1, X2) , activate(n__from(X)) -> from(X) , from(X) -> cons(X, n__from(s(X))) , from(X) -> n__from(X) } Obligation: innermost runtime complexity Answer: YES(?,O(1)) The input was oriented with the instance of 'Small Polynomial Path Order (PS,0-bounded)' as induced by the safe mapping safe(2nd) = {}, safe(cons) = {1, 2}, safe(n__cons) = {1, 2}, safe(activate) = {1}, safe(from) = {1}, safe(n__from) = {1}, safe(s) = {1} and precedence activate > cons, activate > from, from > cons . Following symbols are considered recursive: {} The recursion depth is 0. For your convenience, here are the satisfied ordering constraints: cons(; X1, X2) > n__cons(; X1, X2) activate(; X) > X activate(; n__cons(; X1, X2)) > cons(; X1, X2) activate(; n__from(; X)) > from(; X) from(; X) > cons(; X, n__from(; s(; X))) from(; X) > n__from(; X) Hurray, we answered YES(?,O(1))