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