1. For the purposes of article 9, paragraph 1, where three arbitrators are to be appointed and there are multiple parties as claimant or as respondent, unless the parties have agreed to another method of appointment of arbitrators, the multiple parties jointly, whether as claimant or as respondent, shall appoint an arbitrator.
2. If the parties have agreed that the arbitral tribunal is to be composed of a number of arbitrators other than one or three, the arbitrators shall be appointed according to the method agreed upon by the parties.
3. In the event of any failure to constitute the arbitral tribunal under these Rules, the appointing authority shall, at the request of any party, constitute the arbitral tribunal and, in doing so, may revoke any appointment already made and appoint or reappoint each of the arbitrators and designate one of them as the presiding arbitrator.