'Decline the offer (or change one\'s mind).
Args:
party (object): Party declining the deal.
Returns:
did_decline (bool): `True` if there was really an
`accepted` status to change, `False` otherwise.
Notes:
If previously having used the `accept` command, this
function will only work as long as the other party has not
yet accepted.'

def decline(self, party):

    if self.trade_started:
        if (party == self.part_a):
            if self.part_a_accepted:
                self.part_a_accepted = False
                return True
            return False
        elif (party == self.part_b):
            if self.part_b_accepted:
                self.part_b_accepted = False
                return True
            return False
        else:
            raise ValueError
    return False
