Hossein Hajiabolhassan Mojtaba L. Mehrabadi Ruzbeh Tusserkani Tabular graphs and chromatic sum. 11-22 2005 304 Discrete Mathematics 1-3 http://dx.doi.org/10.1016/j.disc.2005.04.022 db/journals/dm/dm304.html#HajiabolhassanMT05