def AR_6(dul):
    """Association release AR-6.

    On receiving P-DATA-TF during attempted association release request
    send P-DATA indication

    State-event triggers: Sta7 + Evt10

    Parameters
    ----------
    dul : dul.DULServiceProvider
        The DICOM Upper Layer Service instance for the local AE

    Returns
    -------
    str
        ``'Sta7'``, the next state of the state machine
    """
    # Issue P-DATA indication
    dul.to_user_queue.put(dul.primitive)

    return 'Sta7'