YES Problem: a(a(f(x,y))) -> f(a(b(a(b(a(x))))),a(b(a(b(a(y)))))) f(a(x),a(y)) -> a(f(x,y)) f(b(x),b(y)) -> b(f(x,y)) Proof: Matrix Interpretation Processor: dim=2 interpretation: [1 0] [b](x0) = [0 0]x0, [1 2] [0] [a](x0) = [0 2]x0 + [2], [f](x0, x1) = x0 + x1 orientation: [1 6] [1 6] [4] [1 2] [1 2] [0] a(a(f(x,y))) = [0 4]x + [0 4]y + [6] >= [0 0]x + [0 0]y + [4] = f(a(b(a(b(a(x))))),a(b(a(b(a(y)))))) [1 2] [1 2] [0] [1 2] [1 2] [0] f(a(x),a(y)) = [0 2]x + [0 2]y + [4] >= [0 2]x + [0 2]y + [2] = a(f(x,y)) [1 0] [1 0] [1 0] [1 0] f(b(x),b(y)) = [0 0]x + [0 0]y >= [0 0]x + [0 0]y = b(f(x,y)) problem: f(a(x),a(y)) -> a(f(x,y)) f(b(x),b(y)) -> b(f(x,y)) Matrix Interpretation Processor: dim=3 interpretation: [1 0 1] [0] [b](x0) = [0 0 0]x0 + [0] [0 0 0] [1], [1 0 0] [0] [a](x0) = [0 0 0]x0 + [0] [0 0 1] [1], [1 0 0] [1 0 1] [f](x0, x1) = [0 0 0]x0 + [0 0 0]x1 [0 0 1] [0 0 0] orientation: [1 0 0] [1 0 1] [1] [1 0 0] [1 0 1] [0] f(a(x),a(y)) = [0 0 0]x + [0 0 0]y + [0] >= [0 0 0]x + [0 0 0]y + [0] = a(f(x,y)) [0 0 1] [0 0 0] [1] [0 0 1] [0 0 0] [1] [1 0 1] [1 0 1] [1] [1 0 1] [1 0 1] [0] f(b(x),b(y)) = [0 0 0]x + [0 0 0]y + [0] >= [0 0 0]x + [0 0 0]y + [0] = b(f(x,y)) [0 0 0] [0 0 0] [1] [0 0 0] [0 0 0] [1] problem: Qed