del: hide in name space;

--- a/src/Pure/facts.ML	Sat Mar 15 22:07:29 2008 +0100
+++ b/src/Pure/facts.ML	Sat Mar 15 22:07:31 2008 +0100
@@ -77,6 +77,9 @@
   in make_facts facts' props' end;
 
 fun del name (Facts {facts = (space, tab), props}) =
-  make_facts (space, Symtab.delete_safe name tab) props;
+  let
+    val space' = NameSpace.hide true name space handle ERROR _ => space;
+    val tab' = Symtab.delete_safe name tab;
+  in make_facts (space', tab') props end;
 
 end;