A Q&A with Michael Gross, author of what curbed.com calls “the definitive tome” on the building, about the late Enid Haupt’s two-bedroom penthouse duplex at 71 East 71st Street, which just hit the market at the mid-bogglingly bubblicious price of $27.5 million. And a prediction of the profit Steve Schwarzman will make when he decides to move on up and trades in his duplex to buy… I dunno… what’s better?… Venus??