NOT EVEN TERTULIANO MÁXIMO AFONSO HIMSELF COULD have said whether sleep once more opened her merciful arms to him after what, to him, had been the terrifying revelation of the existence, possibly in that same city, of a man who, to judge by his face and by his general appearance, was his very image. After a careful comparison of the photograph from five years ago with the close-up of the clerk in the film, and after finding no difference, however tiny, between the two, not even the smallest line present in one and absent in the other, Tertuliano Máximo Afonso fell onto the sofa, not into the armchair, which was not large enough to contain the physical and moral collapse of his body, and there, head in hands, nerves exhausted, stomach churning, he struggled to put his thoughts in order, untangling them from the chaos of emotions that had accumulated since the moment when memory, watching without his knowledge from behind the closed curtain of his eyelids, had woken him with a start from his initial and only sleep. What troubles me most, he finally managed to think, isn't so much the fact that the guy resembles me, is a copy, you might say, a duplicate of me, that's not so very unusual, there are twins, for example, there are look-alikes, species do repeat themselves, the human being repeats itself, head, trunk, arms, legs, and it could happen, although I can't be sure, it's just a hypothesis, that some unforeseen change in a particular genetic group could result in the creation of a being similar to one generated by another entirely unrelated genetic group, that doesn't trouble me as much as knowing that five years ago I was the same as he was then, I mean, both of us even had mustaches, and more than that, the possibility, or, rather, the probability that five years on, that is, now, right now, at this precise hour in the morning, that sameness continues, as if a change in me would occasion the same change in him, or worse still, that one of us changes not because the other one changes, but because any change is simultaneous, that's enough to send you stark staring mad, yes, all right, I mustn't make this into a tragedy, we know that everything that can happen will happen, but, first, there was the chance event that made us the same, then there was the chance event of my seeing a film I'd never even heard of, I could have lived out the rest of my life never imagining that a phenomenon like this would choose to manifest itself in an ordinary teacher of history, a man who only a few hours earlier was correcting his students' mistakes and who now doesn't know what to do with the mistake into which he himself, from one moment to the next, has seen himself transformed. Am I really a mistake, he wondered, and supposing I am, what significance, what consequences does it have for a human being to know that he's a mistake. A shiver of fear ran down his spine and he thought that some things were better left just as they are, to be what they are, because otherwise there is the danger that other people will notice and, even worse, that we too will begin to see through their eyes the hidden blunder that corrupted us at birth and which waits, impatiently chew ing its nails, for the day when it can show itself and say, Here I am. The excessive weight of such deep thought, centered as it was on the possibility of the existence of absolute doubles, albeit intuited in brief flashes rather than put into words, made his head slowly droop and, eventually, sleep, a sleep that, in its own way, would continue the mental labors carried out up until then by wakefulness, overwhelmed his weary body and helped it make itself comfortable on the sofa cushions. Not that it was a rest that merited and justified that sweet name, for after a few moments, Tertuliano Máximo Afonso suddenly opened his eyes, like a talking doll whose mechanism has gone wrong, and repeated, in different words this time, the question he had just asked, What does it mean, being a mistake. He shrugged, as if the question had abruptly ceased to interest him. Whether this indifference was the understandable effect of extreme tiredness or, on the contrary, the beneficent consequence of that brief sleep, it is, nonetheless, both disconcerting and unacceptable because, as we well know, and he better than anyone, the problem was not resolved, it's still there untouched, waiting inside the VCR, having put into words that no one heard but which were there beneath the surface of the scripted dialogue, One of us is a mistake, that was what the clerk at the reception desk actually said to Tertuliano Máximo Afonso when, addressing the actress playing Inés de Castro, he informed her that the room reserved for her was number twelve-eighteen. How many unknown factors are there in this equation, the history teacher asked the mathematics teacher as he was once more crossing the threshold of sleep. His numerate colleague did not answer his question, he merely looked at him pityingly and said, We'll talk about it later, rest now, try to get some sleep, you need it. Sleep was indeed what Tertuliano Máximo Afonso most wanted at that moment, but the attempt failed. Soon afterward, he was awake again, full of the brilliant idea that had suddenly occurred to him, which was to ask his colleague in mathematics to tell him why he had suggested watching