is the Laplace differential operator, and the function T (x,y) satisfies a Dirichlet boundary condition: T (x,y) = o along the legs of the triangle. Lamé's solution to this problem, the letter went on, was based on a very broad discourse on the geometries that lead to characteristic functions expressed with the help of sines and cosines. The most incredible, and for me the most intriguing aspect of this figure, the letter continued, is that characteristic functions expressed using combinations of sines and cosines ordinarily appear in rectangular geometries, and not in the triangle. In fact Lamé, and here I'll finish, didn't prove his formula. Pinsky did, using the technique of functional analysis, and there still is no final proof, though it's a matter of days now. And that was it, no signature, no real explanation, at least not for someone who, like me, understands little of mathematics. I read it through once more just in case. I still didn't understand a thing, and I doubt that anything would have changed even if Lamé had been investigating acoustic tunnels with hard walls. I can't believe the letter is serious, I said to the person who had run into Dragan Mišović from time to time, because if it were serious, he would've at least made a stab at articulating things in a manner accessible to ordinary mortals. That's what he's like, the person said, adding that she was certain he was sincere in his response. He simply sees the world his own way and doesn't understand that no one else sees it as he does. In other words, I said, he genuinely believes what he wrote. Just that, said the person, just that. That was how he was, she added, before I moved up to Banovo Brdo and lost touch with him, though there is no reason to assume that anything has changed in his life. We're often inclined, she said, to assume, when we feel like changing, that everybody else is changing too, just as she was convinced, because she had moved to Banovo Brdo, that Dragan Mišović was no longer taking his regular walks near the former underpass, where she had run into him from time to time, or that her neighbor from the building where she used to live had stopped emptying ashtrays out the window, which was, of course, a delusion, because even when we have left a place, nothing changes there, the cigarette butts continue to fly from the fifth floor, the ashes waft through the air, and Dragan Mišović cautiously paces the streets, skirting the puddles, the litter, the cracks in the pavement. So what now, I thought when the conversation ended, what path should I take? The question was, in fact, the wrong one, because I saw no path ahead. I could have gone back and walked along the pathways I had abandoned, but that looked like a futile ritual with no value other than the very act of repetition. So I decided to stay at home for a few days. I got up early, had coffee and read the paper, worked on the translation of a Pinter play in the morning, wrote or at least tried to write stories in the afternoon, and in the evening I sat in the armchair, in the dark, and listened to recordings of John Martin, Tom Waits, and the bands Weather Report and Steely Dan. I smoked hashish and watched it get dark outside. The lights flicked on in apartments, in some places you could see people sitting at tables or in front of television sets, the streets emptied, there was a longer interval between buses coming and going. On Sunday I wrote a new piece for my