====== Dif operator ======
{{tag>operators}}
===== Description =====
Implementing \=

**Source**:  The Art of Prolog
===== Download =====
Program source code: {{dif_operator.pl}}
===== Listing =====
<code prolog>
/*
   X \= Y :- X and Y are not unifiable.
*/
	:- op(700, xfx, \=).

     X \= X :- !, fail.
     X \= Y.

%  Program 11.8   Implementing \=


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