Planar lattices and equilateral polygons

Abstract If a planar lattice contains the vertices of a convex equilateral n -gon for some n ≠ 4 , then the lattice is similar to a sublattice of Z 5 in R 5 , and it contains the vertices of a convex equilateral 2 n -gon for every n ≥ 2 . If a planar lattice contains the vertices of an equilateral triangle, then the lattice is similar to a sublattice of Z 3 in R 3 , and it contains the vertices of a convex equilateral n -gon for every n ≥ 3 .