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

@@ -148,16 +148,15 @@ 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:
-            specialise_value_list.append(model)
-            # only add those who matches the portal type given
-            if model in child_visited_trade_condition_list:
-              visited_trade_condition_list.append(model)
+        # don't add model that have already been visited. This permit to
+        # visit all the tree and to prevent having circular dependency
+        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:
+            visited_trade_condition_list.append(model)
 
       return visited_trade_condition_list