Liliana Alcón Celina M. Herrera de Figueiredo Márcia R. Cerioli Marisa Gutierrez João Meidanis 17-23 2004 18 Electronic Notes in Discrete Mathematics http://dx.doi.org/10.1016/j.endm.2004.06.003 db/journals/endm/endm18.html#AlconFCGM04