2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/30535The recent result that n congruent balls in R^d have at most 4 distinct geometric permutations is described.To appear in SIGACT News and in Internat. J. Comput. Geom. ApplComputational GeometryDiscrete MathematicsF.2.2; G.2.1text