Azarbaijan Shahid Madani University Communications in Combinatorics and Optimization 2538-2128 7 1 2022 06 01 A counterexample to a conjecture of Jafari Rad and Volkmann 91 92 14219 10.22049/cco.2021.27226.1214 EN Mostafa Blidia Department of Mathematics, University of Blida 1. B.P. 270, Blida, Algeria Mustapha Chellali Department of Mathematics, University of Blida 1. B.P. 270, Blida, Algeria Journal Article 2021 04 22 In this short note, we disprove the conjecture of Jafari Rad and Volkmann<br />that every $\gamma $-vertex critical graph is $\gamma _{R}$-vertex critical,<br />where $\gamma (G)$ and $\gamma _{R}(G)$ stand for the domination number and<br />the Roman domination number of a graph $G$, respectively. γ -vertex critical graphs γ _{R}-vertex critical graphs Roman domination https://comb-opt.azaruniv.ac.ir/article_14219_d105f0d530108e7b8c566d7db0a2b731.pdf