1. E. J. Cockayne, Domination of undirected graphs. A survey. In theory and applications of graphs, Lecture notes in Mathematics, springer-verlag, 642 (1978) 141–47.
2. G. Chartrand, F. Harary and B. G. Yu, On the out-domination and in-domination of a digraph, Discrete Mathematics, 197(198) (1999) 179–183.
3. G. Chartrand and Ping Zhang, Introduction to graph Theory, Tata Mc.Graw.Hill Edition, (2006).
4. Jorgen Bang-Jensen and Gregory Gutin, Digraphs theory, algorithms and applications, Springer-Verlag, Newyork, (2007).
5. J. Bondy and A. Murty, Graph theory and applications, Newyork: North Holland, (1986).