Rewriting of a cryptic comment.

acs/abac/models.py

@@ -340,10 +340,15 @@ class AbacRule(models.Model):
         predicates2 = {}
         expression = self.expression
         '''
-            Pb if a predicate id is equal to value.
-            The value of the predicate will be substitue with a predicate
-            with that id.
-            Solution: make a first substitution with unique identifiers.
+            Here we substitute primary keys with the predicate description.
+
+            The substitution might fail if some descriptions contains
+            primary keys since with an iterative substitution, a
+            primary key resulting from a previsous substitution would be
+            replaced by another description.
+
+            To prevent this we realize a two-round substitution with unique
+            identifiers.
         '''
         for p in Predicate.objects.filter(rule=self):
             rdm_str = ''.join(\