Wife swapping: it's hard to make binding contracts for repugnant transactions

The following comes from Al Roth's Market Design blog:

Yannai Gonczarowski writes:

"A week ago, the following question was asked on a popular Israeli web forum that discusses legal questions: The author says that he and his wife agreed with their neighbor and his wife that they will exchange partners for a day: the neighbor will be with the author's wife for one day, and after the neighbor's wife returns from her current trip abroad, she will be with the author for a day. As you can already imagine, the author writes that the first part happened, but when the neighbor's wife returned from abroad, the neighbor and his wife denied any such agreement and ignored the author's messages. The author says that he has text messages on his phone to prove the agreement and that he spent a considerable amount of money on beverages for the intended day with the neighbor's wife, and asks the readers of the web forum whether he has a cause for legal action against the neighbor and his wife for violating the agreement.

A link to the question on the web forum (the actual Hebrew text is somewhat more colorful/offensive): http://www.lawforums.co.il/SingleMessage.aspx?MessageID=1186029

There is sometimes is a real difference between sequential and simultaneous move games.