NO Problem: a(x1) -> x1 a(b(x1)) -> a(c(b(b(a(a(x1)))))) b(x1) -> x1 c(c(x1)) -> x1 Proof: String Reversal Processor: a(x1) -> x1 b(a(x1)) -> a(a(b(b(c(a(x1)))))) b(x1) -> x1 c(c(x1)) -> x1 Unfolding Processor: loop length: 7 terms: b(a(c(a(x1821)))) a(a(b(b(c(a(c(a(x1821)))))))) a(a(b(b(c(c(a(x1821))))))) a(a(b(b(a(x1821))))) a(a(b(a(a(b(b(c(a(x1821))))))))) a(a(b(a(b(b(c(a(x1821)))))))) a(a(b(a(b(c(a(x1821))))))) context: a(a([])) substitution: x1821 -> x1821 Qed