In making the appointment, the appointing authority shall use the following list - procedure, unless the parties agree that the list - procedure should not be used or unless the appointing authority determines in its discretion that the use of the list - procedure is not appropriate for the case: (a) The appointing authority shall communicate to each of the parties an
identical list containing at least three names; (b) Within 15 days after the receipt of this list, or such other period as may be set by the Secretariat, each party may return the list to the appointing authority, without
copying the other party, after having deleted the name or names to which it objects and numbered the remaining names on the list in the order of its preference; (c) After the expiration of the above period of time the appointing authority shall appoint the sole arbitrator from
among the names approved on the lists returned to it and in accordance with the order of preference indicated by the parties; (d) If for any reason the appointment can not be made according to this procedure, the appointing authority may exercise its discretion in appointing the sole arbitrator.