YES Problem: b(a(a(x1))) -> a(b(c(x1))) c(a(x1)) -> a(c(x1)) b(c(a(x1))) -> a(b(c(x1))) c(b(x1)) -> b(a(x1)) a(c(b(x1))) -> c(b(a(x1))) Proof: String Reversal Processor: a(a(b(x1))) -> c(b(a(x1))) a(c(x1)) -> c(a(x1)) a(c(b(x1))) -> c(b(a(x1))) b(c(x1)) -> a(b(x1)) b(c(a(x1))) -> a(b(c(x1))) KBO Processor: weight function: w0 = 1 w(c) = w(a) = 1 w(b) = 0 precedence: b > a > c problem: Qed