sveral updates

git-svn-id: https://yap.svn.sf.net/svnroot/yap/trunk@1415 b08c6af1-5177-4d33-ba66-4b1c6b8b522a

library/ordsets.yap

@@ -36,9 +36,14 @@
 	ord_symdiff/3,		%  Set x Set -> Set
         ord_union/2,            %  Set^2 -> Set
 	ord_union/3,		%  Set x Set -> Set
-	ord_union/4		%  Set x Set -> Set x Set
+	ord_union/4,		%  Set x Set -> Set x Set,
+	ord_empty/1,             % -> Set
+	ord_memberchk/2             % Element X Set
       ]).
 
+:- use_module(library(lists),
+   [memberchk/2]).
+
 /*
 :- mode
 	list_to_ord_set(+, ?),
@@ -347,3 +352,8 @@ ord_union_all(N,Sets0,Union,Sets) :-
        ord_union(X, Y, Union)
     ).
 
+ord_empty([]).
+
+ord_memberchk(Element, Set) :-
+	memberchk(Element, Set).
+