YES Problem: a(a(b(b(x1)))) -> b(b(c(c(a(a(x1)))))) b(b(c(c(x1)))) -> c(c(b(b(b(b(x1)))))) b(b(a(a(x1)))) -> a(a(c(c(b(b(x1)))))) Proof: String Reversal Processor: b(b(a(a(x1)))) -> a(a(c(c(b(b(x1)))))) c(c(b(b(x1)))) -> b(b(b(b(c(c(x1)))))) a(a(b(b(x1)))) -> b(b(c(c(a(a(x1)))))) Matrix Interpretation Processor: dim=3 interpretation: [1 0 0] [0] [a](x0) = [0 0 1]x0 + [1] [0 1 0] [0], [1 0 1] [0] [b](x0) = [1 0 0]x0 + [1] [0 0 1] [0], [1 0 0] [c](x0) = [0 1 0]x0 [0 0 0] orientation: [1 0 2] [2] [1 0 2] [0] b(b(a(a(x1)))) = [1 0 1]x1 + [2] >= [1 0 1]x1 + [2] = a(a(c(c(b(b(x1)))))) [0 0 1] [1] [0 0 0] [1] [1 0 2] [0] [1 0 0] [0] c(c(b(b(x1)))) = [1 0 1]x1 + [1] >= [1 0 0]x1 + [1] = b(b(b(b(c(c(x1)))))) [0 0 0] [0] [0 0 0] [0] [1 0 2] [0] [1 0 0] [0] a(a(b(b(x1)))) = [1 0 1]x1 + [2] >= [1 0 0]x1 + [1] = b(b(c(c(a(a(x1)))))) [0 0 1] [1] [0 0 0] [0] problem: c(c(b(b(x1)))) -> b(b(b(b(c(c(x1)))))) a(a(b(b(x1)))) -> b(b(c(c(a(a(x1)))))) WPO Processor: algebra: Sum weight function: w0 = 0 w(c) = w(a) = w(b) = 0 status function: st(c) = st(a) = st(b) = [0] precedence: a > c > b problem: Qed