YES Problem: a(a(x1)) -> b(c(x1)) b(b(x1)) -> c(d(x1)) c(c(x1)) -> d(d(d(x1))) d(d(d(x1))) -> a(c(x1)) Proof: Arctic Interpretation Processor: dimension: 1 interpretation: [d](x0) = 6x0, [b](x0) = 8x0, [c](x0) = 9x0, [a](x0) = 9x0 orientation: a(a(x1)) = 18x1 >= 17x1 = b(c(x1)) b(b(x1)) = 16x1 >= 15x1 = c(d(x1)) c(c(x1)) = 18x1 >= 18x1 = d(d(d(x1))) d(d(d(x1))) = 18x1 >= 18x1 = a(c(x1)) problem: c(c(x1)) -> d(d(d(x1))) d(d(d(x1))) -> a(c(x1)) Arctic Interpretation Processor: dimension: 2 interpretation: [1 -&] [d](x0) = [0 2 ]x0, [2 -&] [c](x0) = [2 3 ]x0, [0 -&] [a](x0) = [1 0 ]x0 orientation: [4 -&] [3 -&] c(c(x1)) = [5 6 ]x1 >= [4 6 ]x1 = d(d(d(x1))) [3 -&] [2 -&] d(d(d(x1))) = [4 6 ]x1 >= [3 3 ]x1 = a(c(x1)) problem: c(c(x1)) -> d(d(d(x1))) Arctic Interpretation Processor: dimension: 3 interpretation: [0 -& 0 ] [d](x0) = [-& -& 0 ]x0 [0 0 0 ] , [0 1 0 ] [c](x0) = [1 0 1 ]x0 [1 1 -&] orientation: [2 1 2] [0 0 0] c(c(x1)) = [2 2 1]x1 >= [0 0 0]x1 = d(d(d(x1))) [2 2 2] [0 0 0] problem: Qed