Jack and his sister Lisa inherited their parent’s cottage. Jack suggested to Lisa that he would be willing to buy her out for $50 000. Lisa thought about it for a minute and then quickly agreed. “A deal is a deal,” said Lisa and shook hands with her brother. “There is no need for us to go to a lawyer and get a big fancy contract written up.” If Lisa ever has to prove this contract in a court of law, what are the problems she faces?