YES(O(1),O(n^1)) We are left with following problem, upon which TcT provides the certificate YES(O(1),O(n^1)). Strict Trs: { first(0(), X) -> nil() , first(s(X), cons(Y)) -> cons(Y) , from(X) -> cons(X) } Obligation: innermost runtime complexity Answer: YES(O(1),O(n^1)) We use the processor 'Small Polynomial Path Order (PS,1-bounded)' to orient following rules strictly. Trs: { first(0(), X) -> nil() , first(s(X), cons(Y)) -> cons(Y) , from(X) -> cons(X) } The induced complexity on above rules (modulo remaining rules) is YES(?,O(n^1)) . These rules are moved into the corresponding weak component(s). Sub-proof: ---------- The input was oriented with the instance of 'Small Polynomial Path Order (PS,1-bounded)' as induced by the safe mapping safe(first) = {1, 2}, safe(0) = {}, safe(nil) = {}, safe(s) = {1}, safe(cons) = {1}, safe(from) = {} and precedence first ~ from . Following symbols are considered recursive: {first} The recursion depth is 1. For your convenience, here are the satisfied ordering constraints: first(; 0(), X) > nil() first(; s(; X), cons(; Y)) > cons(; Y) from(X;) > cons(; X) We return to the main proof. We are left with following problem, upon which TcT provides the certificate YES(O(1),O(1)). Weak Trs: { first(0(), X) -> nil() , first(s(X), cons(Y)) -> cons(Y) , from(X) -> cons(X) } Obligation: innermost runtime complexity Answer: YES(O(1),O(1)) Empty rules are trivially bounded Hurray, we answered YES(O(1),O(n^1))