Martin Farber Gena Hahn Pavol Hell Donald J. Miller Concerning the achromatic number of graphs. 21-39 1986 40 J. Comb. Theory, Ser. B 1 http://dx.doi.org/10.1016/0095-8956(86)90062-6 db/journals/jct/jctb40.html#FarberHHM86