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