YES 1: H(H(x1)) -> K(x1) 2: H(K(x1)) -> K(H(x1)) @Rule Labeling --- R 1: H(H(x1)) -> K(x1) 2: H(K(x1)) -> K(H(x1)) --- S 1: H(H(x1)) -> K(x1) 2: H(K(x1)) -> K(H(x1))