MAYBE
0.08/0.17	MAYBE
0.08/0.17	
0.08/0.17	Problem:
0.08/0.17	 ackin(s(X),s(Y)) -> u21(ackin(s(X),Y),X)
0.08/0.17	 u21(ackout(X),Y) -> u22(ackin(Y,X))
0.08/0.17	
0.08/0.17	Proof:
0.08/0.17	 Open
0.08/0.17	EOF