====== Ackermann ======
{{tag>function}}
===== Description =====
Program calculate Ackermann's function

**Source**:  The Art of Prolog
===== Download =====
Program source code: {{prolog:pllib:ackermann.pl}}
===== Listing =====
<code prolog>
/*
	ackermann(X,Y,A) :-
		A is the value of Ackermann's function for
		the natural numbers X and Y.
*/

	ackermann(0,N,s(N)).
	ackermann(s(M),0,Val) :- ackermann(M,s(0),Val).
	ackermann(s(M),s(N),Val) :-
		ackermann(s(M),N,Val1), ackermann(M,Val1,Val).

%	Program 3.9: Ackermann's function

</code>
===== Comments =====