Merge pull request #49 from Haru0517/master

Fix `X` to anonymous variable in `greater_than`

Author: dragonwasrobot

chapter-03/exercises.pl

@@ -28,7 +28,7 @@
 %% ?- greater_than(succ(succ(succ(0))),succ(0)). -> true
 %% ?- greater_than(succ(succ(0)),succ(succ(succ(0)))). -> no
 
-greater_than(succ(X),0).
+greater_than(succ(_),0).
 greater_than(succ(X),succ(Y)) :-
   greater_than(X,Y).