On a motion to compel arbitration brought by a defendant computer manufacturer in a case alleging design defects brought as a putative consumer class action by a purchaser, the district court's judgment denying the motion is vacated and the case remanded, where: 1) the arbitration agreement in the purchase contract did not indicate the parties' unambiguous intent not to arbitrate their disputes if the named arbitrator was unavailable; and 2) Section 5 of the Federal Arbitration Act requires a court to address such unavailability by appointing a substitute arbitrator.