YES Problem: minus(minus(x)) -> x minux(+(x,y)) -> +(minus(y),minus(x)) +(minus(x),+(x,y)) -> y +(+(x,y),minus(y)) -> x Proof: Matrix Interpretation Processor: dim=1 interpretation: [minux](x0) = 4x0 + 2, [+](x0, x1) = x0 + x1, [minus](x0) = 4x0 + 1 orientation: minus(minus(x)) = 16x + 5 >= x = x minux(+(x,y)) = 4x + 4y + 2 >= 4x + 4y + 2 = +(minus(y),minus(x)) +(minus(x),+(x,y)) = 5x + y + 1 >= y = y +(+(x,y),minus(y)) = x + 5y + 1 >= x = x problem: minux(+(x,y)) -> +(minus(y),minus(x)) Matrix Interpretation Processor: dim=3 interpretation: [1 0 1] [0] [minux](x0) = [0 0 0]x0 + [0] [0 0 0] [1], [1 0 0] [1 0 0] [0] [+](x0, x1) = [0 0 0]x0 + [0 0 0]x1 + [0] [0 0 0] [0 0 0] [1], [1 0 0] [minus](x0) = [0 0 0]x0 [0 0 0] orientation: [1 0 0] [1 0 0] [1] [1 0 0] [1 0 0] [0] minux(+(x,y)) = [0 0 0]x + [0 0 0]y + [0] >= [0 0 0]x + [0 0 0]y + [0] = +(minus(y),minus(x)) [0 0 0] [0 0 0] [1] [0 0 0] [0 0 0] [1] problem: Qed