YES O(n^3) TRS: { a(X) -> e(), b(X) -> e(), c(X) -> e(), c(b(a(X))) -> a(a(b(b(c(c(X)))))) } DUP: We consider a non-duplicating system. Trs: { a(X) -> e(), b(X) -> e(), c(X) -> e(), c(b(a(X))) -> a(a(b(b(c(c(X)))))) } Matrix Interpretation: Interpretation class: triangular [0] [e] = [0] [0] [X2] [1 1 0][X2] [1] [c]([X1]) = [0 1 0][X1] + [0] [X0] [0 0 0][X0] [2] [X2] [1 0 0][X2] [2] [b]([X1]) = [0 0 3][X1] + [0] [X0] [0 0 0][X0] [0] [X2] [1 2 0][X2] [1] [a]([X1]) = [0 0 0][X1] + [0] [X0] [0 0 0][X0] [2] Qed