YES Problem: a(b(a(x1))) -> a(a(b(b(a(a(x1)))))) b(a(a(b(x1)))) -> b(a(b(x1))) Proof: Matrix Interpretation Processor: dim=3 interpretation: [1 0 0] [0] [b](x0) = [0 0 0]x0 + [0] [0 1 0] [1], [1 0 1] [0] [a](x0) = [0 0 0]x0 + [1] [0 0 0] [0] orientation: [1 0 1] [2] [1 0 1] [1] a(b(a(x1))) = [0 0 0]x1 + [1] >= [0 0 0]x1 + [1] = a(a(b(b(a(a(x1)))))) [0 0 0] [0] [0 0 0] [0] [1 1 0] [1] [1 1 0] [1] b(a(a(b(x1)))) = [0 0 0]x1 + [0] >= [0 0 0]x1 + [0] = b(a(b(x1))) [0 0 0] [2] [0 0 0] [2] problem: b(a(a(b(x1)))) -> b(a(b(x1))) Arctic Interpretation Processor: dimension: 2 interpretation: [b](x0) = x0, [1 -&] [a](x0) = [3 -&]x0 orientation: [2 -&] [1 -&] b(a(a(b(x1)))) = [4 -&]x1 >= [3 -&]x1 = b(a(b(x1))) problem: Qed