Reservation Telephone Cooperative; Consolidated Telephonecooperative; West River Telecommunicationscooperative, Plaintiffs-appellants,mountrail-williams Electric Cooperative, Plaintiff,jay Sandstrom; A. Neal Hendrickson, Plaintiffs-intervenors, v. Three Affiliated Tribes of the Fort Berthold Reservation;three Affiliated Tribes Tribal Business Council; Threeaffiliated Tribes Tax Commission; Wilbur D. Wilkinson,chairman, Tribal Business Council; Joseph J. Walker,director, Tax Commission, Defendants-appellees.state of North Dakota; United States of America, Amicus Curiae