On the Dirichlet—Voronoi cell of unimodular lattices

This paper consists of two results concerning the Dirichlet-Voronoi cell of a lattice. The first one is a geometric property of the cell of an integral unimodular lattice while the second one gives a characterization of all those lattice vectors of an arbitrary lattice whose multiples by 1/2 are on the boundary of the cell containing the origin. This result is a generalization of a well-known theorem of Voronoi characterizing the so-called relevants of the cell.