Rocky Mountain Races, Inc., sponsors the "Pioneer Trail Ultramarathon," with an advertised first prize of $10,000. The rules require the competitors to run one hundred miles from the floor of blackwater Canyon to the top of Pinnacle Mountain. The rules also provide that Ricky reserves the right to have the terms of the race at any time. Monica enters the race and is declared the winner. Rocky offers her a prize of $1,000 instead of $10,000. Did Rocky and Monica have a contract? State the rule of law you are relying on and fully define it when answering the question.