YES O(n^4) 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] [0] [e] = [0] [0] [X3] [1 0 1 1][X3] [1] [X2] [0 0 1 1][X2] [0] [c]([X1]) = [0 0 0 1][X1] + [0] [X0] [0 0 0 0][X0] [0] [X3] [1 1 1 0][X3] [1] [X2] [0 0 0 0][X2] [0] [b]([X1]) = [0 0 1 0][X1] + [1] [X0] [0 0 0 0][X0] [1] [X3] [1 0 0 0][X3] [1] [X2] [0 0 1 1][X2] [1] [a]([X1]) = [0 0 0 1][X1] + [1] [X0] [0 0 0 0][X0] [0] Qed