[WWcvs] pg: Added sets to the differentiation information (no derivatives

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

Log Message:
-----------
Added sets to the differentiation information (no derivatives allowed)

Modified Files:
--------------
    pg/lib/Parser:
        Differentiation.pm

Revision Data
-------------
Index: Differentiation.pm
===================================================================
RCS file: /webwork/cvs/system/pg/lib/Parser/Differentiation.pm,v
retrieving revision 1.6
retrieving revision 1.7
diff -Llib/Parser/Differentiation.pm -Llib/Parser/Differentiation.pm -u -r1.6 -r1.7
--- lib/Parser/Differentiation.pm
+++ lib/Parser/Differentiation.pm
@@ -662,6 +662,11 @@
   $self->Error("Can't differentiate intervals");
 }
 
+sub Value::Set::D {
+  shift; shift; my $self = shift;
+  $self->Error("Can't differentiate sets");
+}
+
 sub Value::Union::D {
   shift; shift; my $self = shift;
   $self->Error("Can't differentiate unions");