Proof is the latest in a line of garlanded disappointments from Broadway. Last season it won a Tony, a Pulitzer, and various critics' awards for best original script, but only, it seems, because it stood out in the field of new Broadway shows like an overgrown cabbage. It tells the engaging story of a 25-year-old mathematician who spent her most fruitful and creative years nursing her deteriorating father. Now he's dead. She feels bitter, and in a fit of what looks like the same insanity that gripped her father, she claims to have written a groundbreaking mathematical proof. We never learn what the family illness is, although it seems to involve a sharp temper and a lot of shouting. Chelsea Altman plays the daughter, Catherine, in a loud, pissed-off monotone. The father, Robert, is played in flashbacks as an appealingly cranky old genius by Robert Foxworth. The flashback scenes show passages of award-worthy dialogue, and the material itself is interesting. But there are some huge, basic flaws: 1) It's hard to believe that the authorship of a handwritten proof could take so long to verify; 2) bouts of argument come on like sudden squalls, without any setup; and 3) the whole thing ends in a way a mathematician might call truncated. David Auburn has all the laurels the New York establishment can heap on an ambitious playwright, and now, like Tony Kushner, he just needs to master the art of playwriting.