“The Open Couple” is a hilarious and perceptive comedy about a couple who test the boundaries of their relationship. It was also written by a couple: the Italian Nobel prize-winning author, director and actor Dario Fo and his wife, the actor Franca Rame. How open can a relationship be? How subject are relationships to the norms of a given society and class system? Why can’t a man have a wife and a mistress? And what happens when the roles are reversed?