Let's start with the last problem from last week, attributed to Isaac Newton himself: Can 9 trees be planted so that they form 10 straight rows of 3 trees per row? It can be done, as seen in the elegant solution in the attached figure. Solution that, coincidentally (that is to say: in mathematics there are no coincidences), illustrates the Pappus theorem, which shows that if in a pair of lines three points are chosen at random in each one and joined two by two by rectilinear segments, each point of one line with each of the points of the other, the intersections of the segments that join them will be in a straight line.
