YES Problem: a(b(x1)) -> b(b(a(x1))) b(c(x1)) -> c(b(b(x1))) c(a(x1)) -> a(c(c(x1))) Proof: String Reversal Processor: b(a(x1)) -> a(b(b(x1))) c(b(x1)) -> b(b(c(x1))) a(c(x1)) -> c(c(a(x1))) WPO Processor: algebra: Pol weight function: w0 = 0 w(a) = 4 w(c) = 1 w(b) = 0 status function: st(c) = st(a) = st(b) = [0] subterm coefficient function: sc(a, 0) = 3 sc(c, 0) = sc(b, 0) = 1 precedence: c > b > a problem: Qed