[WWcvs] pg: When two sets are added, combine them rather than form a union.

[dpvc v. a. <we...@ma...>]

Log Message:
-----------
When two sets are added, combine them rather than form a union.
(This allows Inequailities context to report errors better when
student answers are of the form x=a or x=b.)

Modified Files:
--------------
    pg/lib/Value:
        Set.pm

Revision Data
-------------
Index: Set.pm
===================================================================
RCS file: /webwork/cvs/system/pg/lib/Value/Set.pm,v
retrieving revision 1.19
retrieving revision 1.20
diff -Llib/Value/Set.pm -Llib/Value/Set.pm -u -r1.19 -r1.20
--- lib/Value/Set.pm
+++ lib/Value/Set.pm
@@ -84,10 +84,11 @@
 #
 
 #
-#  Addition forms additional sets
+#  Addition forms unions (or combines sets)
 #
 sub add {
   my ($self,$l,$r) = Value::checkOpOrderWithPromote(@_);
+  return $self->make($l->value,$r->value) if $l->type eq 'Set' && $r->type eq 'Set';
   Value::Union::form($self->context,$l,$r);
 }
 sub dot {my $self = shift; $self->add(@_)}