Inequalities of Independence Number, Clique Number and Connectivity of Maximal Connected Domination Critical Graphs

Abstract

A $k$-$\gamma_{c}$-edge critical graph is a graph $G$ with the connected domination number $\gamma_{c}(G) = k$ and $\gamma_{c}(G + uv) < k$ for every $uv \in E(\overline{G})$. Further, a $2$-connected graph $G$ is said to be $k$-$\gamma_{c}$-vertex critical if $\gamma_{c}(G) = k$ and $\gamma_{c}(G - v) < k$ for all $v \in V(G)$. A maximal $k$-$\gamma_{c}$-vertex critical graph is a graph which are both $k$-$\gamma_{c}$-edge critical and $k$-$\gamma_{c}$-vertex critical. Let $\kappa, \delta, \omega$ and $\alpha$ be respectively connectivity minimum degree, clique number and independence number. In this paper, we prove that every maximal $3$-$\gamma_{c}$-vertex critical graph $G$ satisfies $\alpha \leq \delta$ and this bound is best possible. We prove further that $G$ satisfies $\alpha + \omega \leq n - 1$ and we also characterize all such graphs achieving the upper bounds. We finally show that if $G$ satisfies $\kappa < \delta$, then every two vertices of $G$ are joined by hamiltonian path.