But before that, and perhaps much earlier, for example a few centimeters from the mouth of the sink, at the height of the apartment on the second floor, or in the first underground pipe, we may happen to find the hair. It is enough to think of the joy that this would cause us, in the astonished calculation of the efforts saved by pure good luck, to choose, to demand practically a similar task, that every conscious teacher should advise to its students from the earliest childhood, instead of drying their souls with the rule of cross-multiplication or the sorrows of Cancha Rayada.