Winner of the 2001 Pulitzer Prize and Tony Award for best play, Proof combines elements of mystery and surprise with old fashioned storytelling. On the eve of her twenty-fifth birthday, Catherine, a troubled young woman, has spent years caring for her brilliant but unstable father, a famous mathematician.

Now, following his death she must deal with her own emotions and the arrival of her estranged sister. Over the long weekend that follows a burgeoning romance and the discovery of a mysterious notebook draws Catherine into the most difficult problem of all: How much of her father's madness or genius will she inherit?