====== Ancestor ======
{{tag>family recursion}}
===== Description =====
The ancestor relationship. 

**Source**:  The Art of Prolog
===== Download =====
Program source code: {{ancestor.pl}}
===== Listing =====
<code prolog>
/*
	ancestor(Ancestor,Descendant)  :-
		Ancestor is an ancestor of Descendant.
*/
	ancestor(Ancestor,Descendant) :-
		parent(Ancestor,Descendant).
	ancestor(Ancestor,Descendant) :-
		parent(Ancestor,Person), ancestor(Person,Descendant).

%	Program 2.5: The ancestor relationship
</code>
===== Comments =====