Triangles in graphs without the expansion of $4$-cycle

Abstract

The expansion $F^{△}$ of a graph $F$ is the graph obtained from $F$ by replacing each edge with a triangle. Lv \etal proposed a conjecture on the maximum number of triangles in a graph without $P_k^{△}$ or $C_k^{△}$ for every $k\ge 4$. Their conjecture was confirmed in previous work for $P_k^{△}$ when $k\ge 4$ and $C_k^{△}$ when $k\ge 5$. In this note, we resolve the remaining case $C_4^{△}$, demonstrating that this is the only counterexample to their conjecture.