Gennian Ge Alan C. H. Ling Group divisible designs with block size four and group type <i>g<sup>u</sup>m</i><sup>1</sup> for small <i>g</i>. 97-120 2004 285 Discrete Mathematics 1-3 http://dx.doi.org/10.1016/j.disc.2004.04.003 db/journals/dm/dm285.html#GeL04