YES Problem: a(x1) -> x1 a(x1) -> b(x1) a(b(c(x1))) -> c(c(a(b(a(x1))))) c(x1) -> x1 Proof: Arctic Interpretation Processor: dimension: 3 interpretation: [0 0 0] [c](x0) = [0 0 0]x0 [0 0 0] , [0 -& -&] [b](x0) = [0 -& 2 ]x0 [-& -& -&] , [1 0 0] [a](x0) = [1 0 3]x0 [0 0 0] orientation: [1 0 0] a(x1) = [1 0 3]x1 >= x1 = x1 [0 0 0] [1 0 0] [0 -& -&] a(x1) = [1 0 3]x1 >= [0 -& 2 ]x1 = b(x1) [0 0 0] [-& -& -&] [2 2 2] [2 2 2] a(b(c(x1))) = [2 2 2]x1 >= [2 2 2]x1 = c(c(a(b(a(x1))))) [2 2 2] [2 2 2] [0 0 0] c(x1) = [0 0 0]x1 >= x1 = x1 [0 0 0] problem: a(x1) -> x1 a(b(c(x1))) -> c(c(a(b(a(x1))))) c(x1) -> x1 String Reversal Processor: a(x1) -> x1 c(b(a(x1))) -> a(b(a(c(c(x1))))) c(x1) -> x1 Matrix Interpretation Processor: dim=2 interpretation: [1 2] [c](x0) = [0 1]x0, [1 1] [0] [b](x0) = [0 2]x0 + [2], [1] [a](x0) = x0 + [0] orientation: [1] a(x1) = x1 + [0] >= x1 = x1 [1 5] [5] [1 5] [2] c(b(a(x1))) = [0 2]x1 + [2] >= [0 2]x1 + [2] = a(b(a(c(c(x1))))) [1 2] c(x1) = [0 1]x1 >= x1 = x1 problem: c(x1) -> x1 Arctic Interpretation Processor: dimension: 3 interpretation: [2 0 0] [c](x0) = [0 2 0]x0 [0 0 1] orientation: [2 0 0] c(x1) = [0 2 0]x1 >= x1 = x1 [0 0 1] problem: Qed