====== Add ======
{{tag>math arithmetic}}
===== Description =====
Multiple uses for plus

**Source**:  The Art of Prolog
===== Download =====
Program source code: {{prolog:pllib:add.pl}}
===== Listing =====
<code prolog>
/*
   myplus(X,Y,Z) :- The sum of the numbers X and Y is Z.
*/
   myplus(X,Y,Z) :- nonvar(X), nonvar(Y), Z is X + Y.
   myplus(X,Y,Z) :- nonvar(X), nonvar(Z), Y is Z - X.
   myplus(X,Y,Z) :- nonvar(Y), nonvar(Z), X is Z - Y.

%   Program 10.1   Multiple uses for plus

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