A salesman, a priest and a mathematician were in a conference. One of them asked, "what is preferrable, a wife or a mistress?".

The salesman immediately said, "a mistress, of course. Less commitment, and more fun".

The priest said, "there is risk of loss, and less moral. So wife"

The mathematician said, "We should have both. That way the wife thinks you are with the mistress and the mistress thinks you are with your wife, but you can be in the office doing mathematics!"