YES O(n^4) TRS: { __(X, nil()) -> X, __(__(X, Y), Z) -> __(X, __(Y, Z)), __(nil(), X) -> X, activate(X) -> X, and(tt(), X) -> activate(X), isNePal(__(I, __(P, I))) -> tt() } DUP: We consider a non-duplicating system. Trs: { __(X, nil()) -> X, __(__(X, Y), Z) -> __(X, __(Y, Z)), __(nil(), X) -> X, activate(X) -> X, and(tt(), X) -> activate(X), isNePal(__(I, __(P, I))) -> tt() } Matrix Interpretation: Interpretation class: triangular [X3] [1 0 0 0][X3] [0] [X2] [0 0 0 0][X2] [1] [isNePal]([X1]) = [0 0 0 0][X1] + [0] [X0] [0 0 0 0][X0] [0] [1] [1] [tt] = [0] [0] [X7] [X3] [1 1 0 0][X7] [1 0 0 0][X3] [0] [X6] [X2] [0 0 0 0][X6] [0 1 0 0][X2] [0] [and]([X5], [X1]) = [0 0 0 0][X5] + [0 0 1 0][X1] + [0] [X4] [X0] [0 0 0 0][X4] [0 0 0 1][X0] [0] [X3] [1 0 0 0][X3] [1] [X2] [0 1 0 0][X2] [0] [activate]([X1]) = [0 0 1 0][X1] + [0] [X0] [0 0 0 1][X0] [0] [0] [0] [nil] = [0] [0] [X7] [X3] [1 1 0 0][X7] [1 0 0 0][X3] [1] [X6] [X2] [0 1 0 0][X6] [0 1 0 0][X2] [1] [__]([X5], [X1]) = [0 0 1 0][X5] + [0 0 1 0][X1] + [0] [X4] [X0] [0 0 0 1][X4] [0 0 0 1][X0] [0] Qed