Graphs with $C_3_-free vertices are not universal fixers

A non-isolated vertex $x\in V(G)$ is called $C_{3}$-free if $x$ belongs to no triangle of $G$. In \cite{BMW} Burger, Mynhardt and Weakley introduced the idea of universal fixers. Let $G=(V,E)$ be a graph with $n$ vertices and $G'$ a copy of $G$. For a bijective function $π:V(G)\mapsto V (G')$, we define the prism $πG$ of $G$ as follows: $V(πG)=V(G)\cup V(G')$ and $E(πG)=E(G)\cup E(G')\cup M_π$, where $M_π=\{uπ(u): u\in V(G)\}$. Let $γ(G)$ be the domination number of $G$. If $γ(πG)=γ(G)$ for any bijective function $π$, then $G$ is called a universal fixer. In \cite{MX} it is conjectured that the only universal fixer is the edgeless graph $\bar{K_n}$. In this note, we prove that any graph $G$ with $C_3$-free vertices is not a universal fixer graph.

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