YES O(n^2) TRS: { g(empty(), d) -> d, g(cons(x, k), d) -> g(k, cons(x, d)), f(a, empty()) -> g(a, empty()), f(a, cons(x, k)) -> f(cons(x, a), k) } DUP: We consider a non-duplicating system. Trs: { g(empty(), d) -> d, g(cons(x, k), d) -> g(k, cons(x, d)), f(a, empty()) -> g(a, empty()), f(a, cons(x, k)) -> f(cons(x, a), k) } Matrix Interpretation: Interpretation class: triangular [X3] [X1] [1 0][X3] [1 0][X1] [0] [cons]([X2], [X0]) = [0 0][X2] + [0 1][X0] + [1] [X3] [X1] [1 2][X3] [1 3][X1] [2] [f]([X2], [X0]) = [0 1][X2] + [0 1][X0] + [0] [1] [empty] = [0] [X3] [X1] [1 1][X3] [1 0][X1] [0] [g]([X2], [X0]) = [0 1][X2] + [0 1][X0] + [0] Qed