MAYBE
0.08/0.18	MAYBE
0.08/0.18	
0.08/0.18	Problem:
0.08/0.18	 ack_in(0(),n) -> ack_out(s(n))
0.08/0.18	 ack_in(s(m),0()) -> u11(ack_in(m,s(0())))
0.08/0.18	 u11(ack_out(n)) -> ack_out(n)
0.08/0.18	 ack_in(s(m),s(n)) -> u21(ack_in(s(m),n),m)
0.08/0.18	 u21(ack_out(n),m) -> u22(ack_in(m,n))
0.08/0.18	 u22(ack_out(n)) -> ack_out(n)
0.08/0.18	
0.08/0.18	Proof:
0.08/0.18	 Open
0.08/0.18	EOF