Spanning trails with maximum degree at most 4 in $2K_2$-free graphs

A graph is called $2K_2$-free if it does not contain two independent edges as an induced subgraph. Mou and Pasechnik conjectured that every $\frac{3}{2}$-tough $2K_2$-free graph with at least three vertices has a spanning trail with maximum degree at most $4$. In this paper, we confirm this conjecture. We also provide examples for all $t<\frac{5}{4}$ of $t$-tough graphs that do not have a spanning trail with maximum degree at most $4$.