class Heure:
    def __init__(self, heures = 0, minutes = 0):
        assert heures >= 0 and minutes >= 0
        self.heures = heures
        self.minutes = minutes
        self.invariant()

    def incrementer(self):
        self.minutes = self.minutes + 1
        self.invariant()

    def invariant(self):
        assert self.heures >= 0 and self.heures < 24
        assert self.minutes >= 0 and self.minutes < 60