Embedding Semigroups into Groups, and the Asphericity of Semigroups. - Jung R. Cho; Stephen J. Pride (Int. J. Algebra Comput., 1993)

Hadamard 2-groups with arbitrarily large derived length. - Jung R. Cho; Noboru Ito; Pan Soo Kim; Hyo-Seob Sim (Australas. J Comb., 1997)