A franchise agreement between the parent company franchisor and the franchisees who operated 7-Eleven stores said that any dispute between the franchisor and franchisees would be settled by arbiration. A franchisee sued the franchisor in state court, claiming that some actions of the franchisor were in violation of state law concerning franchises. The state supreme court ruled that the issues covered by the state law could be tried in state court and did not have to go to arbitration. What did the U.S. Supreme Court hold about the choice between arbitration and litigation?