Yeow Meng Chee Gennian Ge Alan C. H. Ling Group Divisible Codes and Their Application in the Construction of Optimal Constant-Composition Codes of Weight Three http://arxiv.org/abs/0807.2680 2008 CoRR abs/0807.2680 db/journals/corr/corr0807.html#abs-0807-2680 informal publication