YES(?,O(n^2)) Problem: not(true()) -> false() not(false()) -> true() odd(0()) -> false() odd(s(x)) -> not(odd(x)) +(x,0()) -> x +(x,s(y)) -> s(+(x,y)) +(s(x),y) -> s(+(x,y)) Proof: Matrix Interpretation Processor: dimension: 2 interpretation: [1 1] [1 1] [4] [+](x0, x1) = [0 1]x0 + [0 1]x1 + [0], [0] [s](x0) = x0 + [1], [1 8] [1] [odd](x0) = [0 0]x0 + [2], [0] [0] = [0], [0] [false] = [0], [1 0] [7] [not](x0) = [0 0]x0 + [2], [0] [true] = [2] orientation: [7] [0] not(true()) = [2] >= [0] = false() [7] [0] not(false()) = [2] >= [2] = true() [1] [0] odd(0()) = [2] >= [0] = false() [1 8] [9] [1 8] [8] odd(s(x)) = [0 0]x + [2] >= [0 0]x + [2] = not(odd(x)) [1 1] [4] +(x,0()) = [0 1]x + [0] >= x = x [1 1] [1 1] [5] [1 1] [1 1] [4] +(x,s(y)) = [0 1]x + [0 1]y + [1] >= [0 1]x + [0 1]y + [1] = s(+(x,y)) [1 1] [1 1] [5] [1 1] [1 1] [4] +(s(x),y) = [0 1]x + [0 1]y + [1] >= [0 1]x + [0 1]y + [1] = s(+(x,y)) problem: Qed