One did not speak of dinner with Andrey Andreyevitch Markov, only the probability of dinner. And that probability might change, of course, depending on whether the great man had taken lunch, or gone without since his usual breakfast of black tea, unripe cantaloupe, and potato knish, or snacked perhaps on a thick slice of that Ukrainian poppyseed cake which Maria Ivanova baked with such flourish. That recipe alone would have made her name in St. Petersburg—if her husband had ever allowed a crumb to leave the house. But Markov was nothing if not meticulous. In my humble opinion, Poisson and…