(EN) J. H. Conway, R. H. Hardin e N. J. A. Sloane, 2, in Packing Lines, Planes, etc.: Packings in Grassmannian Spaces, Experimental Mathematics, vol.5, 1º agosto 2002 [1996], 139.
(EN) J. Conway e N. Sloane, 2 (PDF), in Fast quantizing and decoding and algorithms for lattice quantizers and codes, IEEE Transactions on Information Theory, vol.28, 1982, 227.