YES O(n^5) TRS: { zeros() -> cons(0(), n__zeros()), zeros() -> n__zeros(), activate(X) -> X, activate(n__zeros()) -> zeros(), tail(cons(X, XS)) -> activate(XS) } DUP: We consider a non-duplicating system. Trs: { zeros() -> cons(0(), n__zeros()), zeros() -> n__zeros(), activate(X) -> X, activate(n__zeros()) -> zeros(), tail(cons(X, XS)) -> activate(XS) } Matrix Interpretation: Interpretation class: triangular [X4] [1 0 0 1 1][X4] [1] [X3] [0 1 1 0 0][X3] [0] [tail]([X2]) = [0 0 1 0 0][X2] + [0] [X1] [0 0 0 1 0][X1] [0] [X0] [0 0 0 0 1][X0] [0] [X4] [1 0 0 1 1][X4] [1] [X3] [0 1 0 0 0][X3] [0] [activate]([X2]) = [0 0 1 0 0][X2] + [0] [X1] [0 0 0 1 0][X1] [0] [X0] [0 0 0 0 1][X0] [1] [1] [0] [zeros] = [0] [1] [1] [0] [0] [n__zeros] = [0] [1] [0] [0] [0] [0] = [0] [0] [0] [X9] [X4] [1 0 0 0 0][X9] [1 0 0 0 0][X4] [0] [X8] [X3] [0 0 1 0 0][X8] [0 1 0 0 0][X3] [0] [cons]([X7], [X2]) = [0 0 1 0 0][X7] + [0 0 1 0 0][X2] + [0] [X6] [X1] [0 0 0 0 0][X6] [0 0 0 1 0][X1] [0] [X5] [X0] [0 0 0 0 0][X5] [0 0 0 0 1][X0] [1] Qed