NO Problem: h(f(f(x))) -> h(f(g(f(x)))) f(g(f(x))) -> f(f(x)) Proof: String Reversal Processor: f(f(h(x))) -> f(g(f(h(x)))) f(g(f(x))) -> f(f(x)) Unfolding Processor: loop length: 2 terms: f(f(h(x))) f(g(f(h(x)))) context: [] substitution: x -> x Qed