1. Sotskov, Y.N. and Tanaev, V.S., A Chromatic Polynomial of a Mixed Graph, Proc. Nat. Acad. Sci. Belarus. Phys. Math. Ser., 1976, no. 6, pp. 20–23.
2. Hansen, P., Kuplinsky, J., and de Werra, D., Mixed Graph Colorings, Math. Methods Oper. Res., 1997, vol. 45, pp. 145–160.
3. Reducibility among Combinatorial Problems;R.M. Karp,1972
4. Sotskov, Y.N., Dolgui, A., and Werner, F., Mixed Graph Coloring for Unit-Time Job-Shop Scheduling, Int. J. of Math. Algorithms, 2001, vol. 2, pp. 289–323.
5. Sotskov, Y.N., Tanaev, V.S., and Werner, F., Scheduling Problems and Mixed Graph Colorings, Optimization, 2002, vol. 51, no. 3, pp. 597–624.