Double Dept.: a beautiful hand.(The Talk of the Town)

Dave Bayer's hands are broad and slightly hairy, with wide thumbs and a few small scabs -- abrasions from a recent rock-climbing trip. At first glance, they're nothing special, but when viewed from certain angles they look a lot like Russell Crowe's. "They're not so dissimilar," Bayer, a forty-six-year-old mathematics professor at Barnard College, said the other day, resting his palms on the living-room table in his apartment on Riverside Drive. "Russell's hands are a shade stouter than mine. He's a very athletic guy. I try to be, but you should see him at the gym."

Bayer discovered this manual affinity while working on the film "A Beautiful Mind," which stars Crowe as the mathematician John Forbes Nash, Jr. The director, Ron Howard, hired Bayer as the film's math consultant after reading Bayer's review -- in Notices of the American Mathematical Society -- of the play "Proof," which also explores mathematical genius and madness. (Mary-Louise Parker "convincingly traverses a twodimensional parameter space of personas," Bayer raved.)

It was in rehearsals that Bayer's role took on an extra dimension. "We noticed that Russell Crowe and I had very similar handwriting, and then Ron says, 'Put your hands out,' " Bayer recalled. "At which point Ron said, 'You're the hand double.' And I didn't know what that meant." What it meant was that Bayer's hand, made up to match Crowe's, appeared in closeups shot by the film's second unit.

It took Bayer a while to start thinking like a hand double. Early on, he trimmed his fingernails, even though Crowe was growing his nails longer to make them look more like Nash's, so Bayer had to wear acrylic tips for much of the shoot.

"The cool thing is I got to be the hand double for things that had nothing to do with math," Bayer said. "In the Pentagon scene, where they're moving markers on a map, the closeup where you can actually make out the name of the city -- that was my hand." Bayer also appears in full, albeit briefly, as a professor at the Princeton faculty club.

"Russell does all his own math," Bayer said. "He just can't be there all the time. I do the math while he's ...