2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/164857Given a set of n unit squares in the plane, the goal is to rank them in space in such a way that only few squares see each other vertically. We prove that ranking the squares according to the lexicographic order of their centers results in at most 3n-7 pairwise visibilities for n at least 4. We also show that this bound is best possible, by exhibiting a set of n squares with at least 3n-7 pairwise visibilities under any ranking.4 pages, 2 EPS-figuresComputational GeometryData Structures and Algorithmstext