1. F. Harary, Graph theory (Narosa Publ., New Delhi, 2001).
2. D. B. West et al., Introduction to graph theory, Vol. 2 (Prentice Hall of India, New Delhi, 2001).
3. On the notion of balance of a signed graph.
4. Signed graphs
5. P. Hameed et al., “On co-regular signed graphs,” Australas. J. Combin. 62, 8–16 (2015).