“…It is always possible, up to equivalence, to assume that d = 0; then, two lattices (a, b, c, 0) and (a , b , c , 0) are equivalent if and only if c = c , b = b , a ≡ a (mod b).25 Using Bravais's results, Poincaré asserts that the norm of a lattice is the limit of the ratio of the area of a circle to the number of lattice points inside the circle when the radius increases indefinitely. This allows him to show that the norm of a lattice a group theoretical point of view, see [Scholz 1989]; for a general presentation of Bravais' work using lattices, see [Boucard, Goldstein & Malécot, 2023]. 23 But it is the German version of Selling's paper, published in 1874, and not its French 1877 translation, that Poincaré would mention in [Poincaré 1882b].…”