code: def TENSES(self):
          
          a = set(TENSES[id] for id in self._format)
          a = a.union(set(TENSES[id] for id in self._default.keys()))
          a = a.union(set(TENSES[id] for id in self._default.values()))
          a = sorted(x[:-2] for x in a if x[-2] is False) # Exclude negation.
          return a
docs: Yields a list of tenses for this language, excluding negations.
              Each tense is a (tense, person, number, mood, aspect)-tuple.