MAYBE
23.19/10.18	MAYBE
23.19/10.18	
23.19/10.18	Problem:
23.19/10.18	 f(x,f(y,a())) -> f(f(a(),a()),f(f(x,a()),y))
23.19/10.18	
23.19/10.18	Proof:
23.19/10.18	 Open
23.19/10.19	EOF