Movahedi F.; Akhbari M.H.; Alikhani S.
(2021)
Abstract: Let $$G=(V,E)$$ be a simple graph. A set $$D\subseteq V$$ is a $$2$$-dominating set of $$G$$, if every vertex of $$V\setminus D$$ has at least two neighbors in $$D$$. The $$2$$-domination number of a graph $$G$$, ...