The Grand Manner (Lincoln Center Theater, closes Aug. 1). Superbly acted by Kate Burton and Boyd Gaines and staged with sensitivity and wit by Mark Lamos, A.R. Gurney’s new play looks at first glance like a nostalgia-drenched valentine to Katharine Cornell and the lost world of old-fashioned theater. Don’t be fooled, though. The Grand Manner is really a searching, unexpectedly tough-minded portrait of the “lavender marriage” of a man and a woman who love but don’t desire one another. Smart, funny, poignant (TT).