Triangle-independent sets vs. cuts

A set of edges $T$ in a graph $G$ is triangle-independent if $T$ contains at most one edge from each triangle in $G$. Let $α_1(G)$ denote the maximum size of the triangle-independent set in $G$, and let $τ_B(G)$ denote minimum size of a set $F \subseteq E(G)$ such that $G \setminus F$ is bipartite. We prove that $α_1(G) + τ_B(G) \leq \frac{|V(G)|^2}{4},$ verifying a conjecture due to Lehel, and independently Puleo, and a slightly weaker conjecture of Erdős, Gallai and Tuza. Further, we characterize the graphs which attain the equality.

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