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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 get_lock_amount_after_fees( lock: HashTimeLockState, payee_channel: NettingChannelState, ) -> PaymentWithFeeAmount: """ Return the lock.amount after fees are taken. Fees are taken only for the outgoing channel, which is the one with collateral locked from this node. """

    return PaymentWithFeeAmount(lock.amount - payee_channel.mediation_fee)