diff --git a/tiramisu/config.py b/tiramisu/config.py
index 7fa9e9a..dd0b0f9 100644
--- a/tiramisu/config.py
+++ b/tiramisu/config.py
@@ -669,6 +669,8 @@ def mandatory_warnings(config):
             include_groups=True):
         try:
             config._getattr(path, force_properties=frozenset(('mandatory',)))
+            # XXX raise Exception("ca passe ici")
+            # XXX depuis l'exterieur on donne un paht maintenant ! perturbant !
         except PropertiesOptionError, err:
             if err.proptype == ['mandatory']:
                 yield path
diff --git a/tiramisu/option.py b/tiramisu/option.py
index 383c644..479dbdd 100644
--- a/tiramisu/option.py
+++ b/tiramisu/option.py
@@ -925,9 +925,9 @@ class OptionDescription(BaseInformation):
 def validate_requires_arg(requires, name):
     """check malformed requirements
     and tranform dict to internal tuple
-    
-    :param requires: have a look at the 
-                     :meth:`tiramisu.setting.Settings.apply_requires` method to 
+
+    :param requires: have a look at the
+                     :meth:`tiramisu.setting.Settings.apply_requires` method to
                      know more about
                      the description of the requires dictionnary
     """
@@ -1009,4 +1009,4 @@ def validate_requires_arg(requires, name):
                                      require[5])
             ret_action.append(req)
         ret.append(tuple(ret_action))
-    return tuple(config_action.keys()), tuple(ret)
+    return frozenset(config_action.keys()), tuple(ret)