sets: (A minus (A inter B)) can be be rewritten as (A minus B)

git-svn-id: https://svn.erp5.org/repos/public/erp5/trunk@31508 20353a03-c40f-0410-a6d1-a30d3c3de9de

product/ERP5/Document/TradeCondition.py

@@ -148,12 +148,11 @@ class TradeCondition(Path, Transformation, XMLMatrix):
           # it is possible, that specialised object cannot be specialised
           # anymore
           continue
-        intersection = set(child_specialised_value_list).intersection(\
+        difference = set(child_specialised_value_list).difference(\
             set(visited_trade_condition_list))
-        for model in child_specialised_value_list:
         # don't add model that have already been visited. This permit to
         # visit all the tree and to prevent having circular dependency
-          if model not in intersection:
+        for model in difference:
           specialise_value_list.append(model)
           # only add those who matches the portal type given
           if model in child_visited_trade_condition_list: