make sure list predicates are available to whoever needs them.

pl/init.yap

@@ -52,12 +52,9 @@ otherwise.
 
 :- compile_expressions.
 
-lists:append([], L, L).
-lists:append([H|T], L, [H|R]) :-
-	lists:append(T, L, R).
-
-
 :- [
+    % lists is often used.
+   	 'lists.yap',
    	 'yio.yap',
 	 'debug.yap',
 	 'checker.yap',
@@ -71,6 +68,7 @@ lists:append([H|T], L, [H|R]) :-
 	 'modules.yap',
 	 % must follow grammar
 	 'eval.yap',
+	 'lists.yap',
 	 'signals.yap',
 	 'profile.yap',
 	 'callcount.yap',
@@ -95,24 +93,6 @@ lists:append([H|T], L, [H|R]) :-
 
 :- source.
 
-%   memberchk(+Element, +Set)
-%   means the same thing, but may only be used to test whether a known
-%   Element occurs in a known Set.  In return for this limited use, it
-%   is more efficient when it is applicable.
-
-lists:memberchk(X,[X|_]) :- !.
-lists:memberchk(X,[_|L]) :-
-	lists:memberchk(X,L).
-
-%   member(?Element, ?Set)
-%   is true when Set is a list, and Element occurs in it.  It may be used
-%   to test for an element or to enumerate all the elements by backtracking.
-%   Indeed, it may be used to generate the Set!
-
-lists:member(X,[X|_]).
-lists:member(X,[_|L]) :-
-	lists:member(X,L).
-
 :- no_source.
 
 

pl/lists.yap

@@ -0,0 +1,24 @@
+%   memberchk(+Element, +Set)
+%   means the same thing, but may only be used to test whether a known
+%   Element occurs in a known Set.  In return for this limited use, it
+%   is more efficient when it is applicable.
+
+lists:memberchk(X,[X|_]) :- !.
+lists:memberchk(X,[_|L]) :-
+	lists:memberchk(X,L).
+
+%   member(?Element, ?Set)
+%   is true when Set is a list, and Element occurs in it.  It may be used
+%   to test for an element or to enumerate all the elements by backtracking.
+%   Indeed, it may be used to generate the Set!
+
+lists:member(X,[X|_]).
+lists:member(X,[_|L]) :-
+	lists:member(X,L).
+
+lists:append([], L, L).
+lists:append([H|T], L, [H|R]) :-
+	lists:append(T, L, R).
+
+
+