YES Problem: strict: f(f(x)) -> x weak: f(x) -> g(f(g(f(x)))) Proof: String Reversal Processor: strict: f(f(x)) -> x weak: f(x) -> f(g(f(g(x)))) Matrix Interpretation Processor: dim=2 interpretation: [1 0] [g](x0) = [0 0]x0, [1 1] [0] [f](x0) = [2 0]x0 + [2] orientation: [3 1] [2] f(f(x)) = [2 2]x + [2] >= x = x [1 1] [0] [1 0] [0] f(x) = [2 0]x + [2] >= [2 0]x + [2] = f(g(f(g(x)))) problem: strict: weak: f(x) -> f(g(f(g(x)))) Qed