YES Problem: a(b(b(x1))) -> b(a(a(x1))) a(a(b(x1))) -> b(b(a(x1))) Proof: String Reversal Processor: b(b(a(x1))) -> a(a(b(x1))) b(a(a(x1))) -> a(b(b(x1))) KBO Processor: weight function: w0 = 1 w(a) = w(b) = 1 precedence: b > a problem: Qed