That there shall be established an Italian-Libyan Mixed Arbitration Commission consisting of three mem· bers, one of whom sha:l be appointed by the Government of Italy, one by the Government of Libya and the third by the Secretary-General of the United Nations. The Governments of Italy and Libya shall notify the Secretary-General of the United Nations and each other of the names of their respective arbitrators not later than 15 December 1955; the Secretary-General shall appoint not later than 27 December 1955 the umpire, upon joint designation by Italy and Libya, the said designation to take place not later than 15 December 1955 or, in the event of failure by the parties jointly to submit the name of the umpire by that date, the umpire shall be chosen by the Secretary-General;