'Yields a list of tenses for this language, excluding negations.
Each tense is a (tense, person, number, mood, aspect)-tuple.'

@property
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)))
    return a
