Casey Tompkins: Graphs without cycles of length 0 modulo 4

Bollob\'as proved that for every $k$ and $\ell$ such that $k\mathbb{Z}+\ell$ contains an even number, an $n$-vertex graph containing no cycle of length $\ell \bmod k$ can contain at most a linear number of edges.
The precise (or asymptotic) value of the maximum number of edges in such a graph is known for very few pairs $\ell$ and $k$.
We precisely determine the maximum number of edges in a graph containing no cycle of length $0 \bmod 4$.
This is joint work with Ervin Gy\H{o}ri, Binlong Li, Nika Salia, Kitti Varga and Manran Zhu.

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