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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def lock_reward(self, agreement_id, amount, account):
 """ Lock reward condition. :param agreement_id: id of the agreement, hex str :param amount: Amount of tokens, int :param account: Account :return: bool """

        return self._keeper.lock_reward_condition.fulfill(
            agreement_id, self._keeper.escrow_reward_condition.address, amount, account
        )