[2] Gallai, T: 
Ober extreme Punkt- und Kantenmengen. Annales Univ. Sci. Budapest. Sectio Math., II (1959), 133-138. 
MR 0131370[3] Gupta R. P.: 
Bounds on the chromatic and achromatic numbers of complementary graphs. Recent progress in combinatorics, Academic Press New York and London (1969). 229-235. 
MR 0256930 | 
Zbl 0209.55004[5] Harary F., Hedetniemi S.: 
The achromatic number of a graph. J. of Comb. Theory, 8 (1970), 154-161. 
MR 0253930 | 
Zbl 0195.25702[6] Nordhaus E. A., Gaddum S. W.: 
On complementary graphs. Amer. Math. Monthly, 63 (1956), 175-177. 
MR 0078685 | 
Zbl 0070.18503