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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 is_transaction_expired(transaction, block_number):
 """ True if transaction cannot be mined because it has expired. Some transactions are time dependent, e.g. the secret registration must be done before the lock expiration, and the update transfer must be done before the settlement window is over. If the current block is higher than any of these expirations blocks, the transaction is expired and cannot be successfully executed. """


    is_update_expired = (
        isinstance(transaction, ContractSendChannelUpdateTransfer) and
        transaction.expiration < block_number
    )
    if is_update_expired:
        return True

    is_secret_register_expired = (
        isinstance(transaction, ContractSendSecretReveal) and
        transaction.expiration < block_number
    )
    if is_secret_register_expired:
        return True

    return False