YES Problem: a(a(x1)) -> b(b(b(x1))) b(x1) -> c(c(d(x1))) c(x1) -> d(d(d(x1))) b(c(x1)) -> c(b(x1)) b(c(d(x1))) -> a(x1) Proof: Arctic Interpretation Processor: dimension: 1 interpretation: [c](x0) = 1x0, [d](x0) = x0, [b](x0) = 2x0, [a](x0) = 3x0 orientation: a(a(x1)) = 6x1 >= 6x1 = b(b(b(x1))) b(x1) = 2x1 >= 2x1 = c(c(d(x1))) c(x1) = 1x1 >= x1 = d(d(d(x1))) b(c(x1)) = 3x1 >= 3x1 = c(b(x1)) b(c(d(x1))) = 3x1 >= 3x1 = a(x1) problem: a(a(x1)) -> b(b(b(x1))) b(x1) -> c(c(d(x1))) b(c(x1)) -> c(b(x1)) b(c(d(x1))) -> a(x1) Arctic Interpretation Processor: dimension: 2 interpretation: [c](x0) = x0, [1 0 ] [d](x0) = [-& 1 ]x0, [1 1 ] [b](x0) = [-& 1 ]x0, [2 2 ] [a](x0) = [-& 2 ]x0 orientation: [4 4 ] [3 3 ] a(a(x1)) = [-& 4 ]x1 >= [-& 3 ]x1 = b(b(b(x1))) [1 1 ] [1 0 ] b(x1) = [-& 1 ]x1 >= [-& 1 ]x1 = c(c(d(x1))) [1 1 ] [1 1 ] b(c(x1)) = [-& 1 ]x1 >= [-& 1 ]x1 = c(b(x1)) [2 2 ] [2 2 ] b(c(d(x1))) = [-& 2 ]x1 >= [-& 2 ]x1 = a(x1) problem: b(x1) -> c(c(d(x1))) b(c(x1)) -> c(b(x1)) b(c(d(x1))) -> a(x1) Arctic Interpretation Processor: dimension: 2 interpretation: [0 1] [c](x0) = [0 0]x0, [1 -&] [d](x0) = [0 -&]x0, [3 -&] [b](x0) = [2 3 ]x0, [0 -&] [a](x0) = [0 -&]x0 orientation: [3 -&] [2 -&] b(x1) = [2 3 ]x1 >= [1 -&]x1 = c(c(d(x1))) [3 4] [3 4] b(c(x1)) = [3 3]x1 >= [3 3]x1 = c(b(x1)) [4 -&] [0 -&] b(c(d(x1))) = [4 -&]x1 >= [0 -&]x1 = a(x1) problem: b(c(x1)) -> c(b(x1)) KBO Processor: weight function: w0 = 1 w(c) = w(b) = 1 precedence: b > c problem: Qed