Get Up with It, a double album Miles Davis recorded between 1970 and 1974, and passing a joint back and forth, a joint of marijuana that Marko had grown the year before near his vacation house in Slankamen. Sounds to me, Marko said, as if you had dropped acid and tripped. Nonsense, I answered, and took a drag, it had nothing to do with earthly things, it felt like ascent and submersion at the same time, like being in two places at once. You're losing it, said Marko, maybe you should stop smoking. He passed me the joint, but I shook my head. There is something strange here, I said, I don't know what, but I'm getting a bad feeling. Like I said, Marko laughed, give it up. He stubbed the joint out in the ashtray. That's not what I meant, I went on, I meant everything that happened, the geometric figure, the way it kept cropping up, my search. Marko said nothing. You know, I asked, what I was thinking before I came to see you? How could I? Marko replied. You're the mystic here, not me. I was thinking, I said, that the man deliberately slapped the woman so I'd see it and go after her, follow her. How could he know that, Marko protested, I mean it's not as if you're famous for taking off after injured parties whenever you witness a violent act to, I don't know, I guess, hold their hand. Hey, tell me, he continued, how many times have you done anything like that in your life? This was a first, I answered. Exactly my point, said Marko, so, no matter what you thought, this didn't happen just so someone could lure you into something, and, by the way, you don't even know what that something is. Maybe this is for starters, I answered, maybe I'll only figure out later what's going on, but Marko didn't want to talk about it anymore. He rolled another joint, put the record on again, and talked about how Miles Davis had made the recording. I didn't listen, I was floating on the waves of the homegrown cannabis, and, somewhere inside me, I was back at the scene by the Danube. Something was not quite right: was it the impact of the blow, the movement of the hand delivering the slap and the woman's behavior afterward, the way she staggered and sloshed into the water? They were not in sync; it was as if something else had been agreed upon, as if the man was supposed to hit her harder, and when the moment came, he hit her differently, and the woman, not expecting it, hadn't had the time to adjust and instead reacted the way they had agreed she would react, as if she had genuinely lost her balance from the blow and nearly fallen into the shallows. What about the man in the black trench coat? Why would he disappear so quickly, unless something had gone wrong, different from what they had planned? I didn't mention the man in the black trench coat to Marko, or he would have been truly convinced I had lost my mind. People who buy into conspiracy theories, Marko had told me many times, have a void in their head they don't know what to do with, so they fill it with junk, and sooner or later, they become victims of sketchy plots, secret organizations with one goal only: to drag that person into something that promises to undermine the very foundations of the world. It was here that I caught on to the sound thread of Miles Davis's trumpet and stopped thinking. Had I been home, I would have fallen asleep, but here, at Marko's, I had to struggle to stay on the surface. I stood up and slowly, as if walking under water, got ready to leave. Marko offered me a bed, which I declined. A challenge is better than surrender, I said. Besides, he didn't live far from me, only three blocks of buildings between us and a small park behind the elementary school, but when I got home I was exhausted, as if I had walked fifteen miles. I will not fall asleep, I thought, massaging my calves, but when I woke up the next morning, it was no longer morning, but noon. I put on water for coffee and dashed out to buy fresh bread and a paper. When I came back from the store, I saw something white in the mailbox. I unlocked it and took out a letter with my name written on it in Cyrillic script on the front, and Dragan Mišović written in Latin script on the back. Only a few minutes earlier, when I came down the stairs, I could have sworn there'd been nothing in the mailbox, and so I raced out into the street, looked to the left, looked to the right, no pedestrians in long winter coats, just one kid wearing a baseball cap, but cap or no cap he was not the person I was looking for. I went back up to the apartment, poured the water into the coffeepot, and made my coffee. Though I was dying to know what was in the letter, I first leafed through the newspaper, perused the articles in the crime section, scanned the cultural listings, and tried to solve the chess problem off the top of my head, without the key. I didn't succeed, though it looked so easy at first glance, but whatever I tried, a solution that saved the black pieces kept coming up, and my bishop was more trouble than help. I put aside the paper and reached for the letter. Once again I inspected my name on the front of the envelope and the name of the sender on the back. The letters were obviously written by the same hand, but why one name, mine, was in Cyrillic, and the other in Latin, I will probably never know. I didn't have the patience to slice carefully through the top of the envelope, so I poked my finger in and ripped it open with a single motion. Unlike our two names, the letter was written on a computer, in Latin script, and printed out on a quality printer. I don't know what this is about, the letter began, but I hope I won't be getting caught up in any more nonsense. What could possibly be hiding in such a simple geometric figure, the letter went on, except the futile desire to make reality different from what it is? Reality is reality, and no path can bring one to its other side, where everything is supposed to be different, closer, I guess, to the truth. But that is something, the letter continued, of no interest to me, so I won't speak of it, for triangles and nothing but triangles are the order of the day; or, I should say, the order of the night, because it is night now. As far as the triangle is concerned there is no difference between day and night, of course, that should be obvious to anyone, but one never knows. People construe all sorts of things, even the possibility that within a triangle inscribed within a circle, or a triangle inserted into a triangle, there are answers to questions. A triangle is a triangle, and that's that. It is, however, true that triangular diagrams such as these, the letter continued, are connected to Möbius's barycentric coordinates, which play a role in the chemistry of color, but there is no additional meaning there that could enrich or facilitate an understanding of the figure (sloppily drawn, by the way). Far more interesting is that a very simple transformation of these coordinates gives what we call the Lamé coordinates. Lamé introduced them in his solution to the problem of the cooling of a prism with a base in the shape of an equilateral triangle, then he came upon the same problem in an analysis of the vibrations of an elastic membrane stretched taut over a triangle, and in the end he noticed that the same equation turned up in the description of an acoustic tunnel with soft walls. In brief, it is necessary to solve the eigenvalue problem