Defensive k-alliances in graphs

J. A. Rodriguez-Velazquez, I. G. Yero, J. M. Sigarreta

Let $\Gamma =(V,E)$ be a simple graph. For a nonempty set $X\subseteq V$, and a vertex $v\in V$, ${\delta }_X(v)$ denotes the number of neighbors $v$ has in $X$. A nonempty set $S\subseteq V$…