2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/64552Partial answers are given to two questions. When does a lattice Lambda contain a sublattice Lambda' of index N that is geometrically similar to Lambda? When is the sublattice "clean", in the sense that the boundary of the Voronoi cells for Lambda ' do not intersect Lambda?7 pages; dedicated to H.S.M. CoxeterCombinatoricsNumber Theory11H06 (52C99)text