YES O(n^4) TRS: {p(p(b(a(x0)), x1), p(x2, x3)) -> p(p(b(x2), a(a(b(x1)))), p(x3, x0))} DUP: We consider a non-duplicating system. Trs: {p(p(b(a(x0)), x1), p(x2, x3)) -> p(p(b(x2), a(a(b(x1)))), p(x3, x0))} Matrix Interpretation: Interpretation class: triangular [X3] [1 1 0 0][X3] [0] [X2] [0 0 0 0][X2] [0] [a]([X1]) = [0 0 1 0][X1] + [1] [X0] [0 0 0 0][X0] [0] [X3] [1 0 0 0][X3] [0] [X2] [0 0 0 0][X2] [0] [b]([X1]) = [0 0 1 0][X1] + [0] [X0] [0 0 0 0][X0] [0] [X7] [X3] [1 0 1 0][X7] [1 1 0 0][X3] [0] [X6] [X2] [0 0 0 0][X6] [0 0 1 0][X2] [0] [p]([X5], [X1]) = [0 0 0 0][X5] + [0 0 0 0][X1] + [0] [X4] [X0] [0 0 0 0][X4] [0 0 0 0][X0] [0] Qed