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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 set_time_server(time_server='time.apple.com'):
    '''
    Designates a network time server. Enter the IP address or DNS name for the
    network time server.

    :param time_server: IP or DNS name of the network time server. If nothing
        is passed the time server will be set to the macOS default of
        'time.apple.com'
    :type: str

    :return: True if successful, False if not
    :rtype: bool

    :raises: CommandExecutionError on failure

    CLI Example:

    .. code-block:: bash

        salt '*' timezone.set_time_server time.acme.com
    '''
    cmd = 'systemsetup -setnetworktimeserver {0}'.format(time_server)
    salt.utils.mac_utils.execute_return_success(cmd)

    return time_server in get_time_server()