[1] M. Atapour, R. Hajypory, S.M. Sheikholeslami and L. Volkmann, The signed k-domination number of directed graphs, Cent. Eur. J. Math. 8 (2010), 1048–1057.
[2] W. Chen and E. Song, Lower bounds on several versions of signed domination number, Discrete Math. 308 (2008), 1837–1846.
[3] E.J. Cockayne and C.M. Mynhardt, On a generalization of signed dominating function of graphs, Ars Combin. 43 (1996), 235–245.
[4] D. Delić and C. Wang, Upper signed k-domination in a general graph, Inform. Process. Lett. 110 (2010), 662–665.
[5] J.E. Dunbar, S.T. Hedetniemi, M.A. Henning and A. McRae, Minus domination in graphs, Discrete Math. 199 (1999), 35–47.
[6] J.E. Dunbar, S.T. Hedetniemi, M.A. Henning and P.J. Slater, Signed domination in graphs, Graph Theory, Combinatorics, and Applications, 1 (1995), 311–322.