NO Problem: a(x1) -> x1 a(b(x1)) -> b(c(a(x1))) c(a(c(x1))) -> b(a(a(x1))) Proof: String Reversal Processor: a(x1) -> x1 b(a(x1)) -> a(c(b(x1))) c(a(c(x1))) -> a(a(b(x1))) Unfolding Processor: loop length: 12 terms: b(a(a(a(a(a(a(x162197))))))) a(c(b(a(a(a(a(a(x162197)))))))) a(c(a(c(b(a(a(a(a(x162197))))))))) a(a(a(b(b(a(a(a(a(x162197))))))))) a(a(a(b(a(c(b(a(a(a(x162197)))))))))) a(a(a(b(a(c(a(c(b(a(a(x162197))))))))))) a(a(a(b(a(a(a(b(b(a(a(x162197))))))))))) a(a(a(b(a(a(a(b(a(c(b(a(x162197)))))))))))) a(a(a(b(a(a(a(a(c(b(c(b(a(x162197))))))))))))) a(a(a(b(a(a(a(a(c(b(c(a(c(b(x162197)))))))))))))) a(a(a(b(a(a(a(a(c(b(a(a(b(b(x162197)))))))))))))) a(a(a(b(a(a(a(a(c(a(c(b(a(b(b(x162197))))))))))))))) context: a(a(a([]))) substitution: x162197 -> b(b(a(b(b(x162197))))) Qed