The limit in the $(k+2,k)$-Problem of Brown, Erdős and Sós exists for all $k\ge 2$

Abstract

Let $f^{(r)}(n;s,k)$ be the maximum number of edges of an $r$-uniform hypergraph on~$n$ vertices not containing a subgraph with $k$~edges and at most $s$~vertices. In 1973, Brown, Erdős and Sós conjectured that the limit $$\underset{n\to \infty }{\lim }{n}^{-2}{f}^{(3)}(n;k+2,k)$$ exists for all positive integers $k\ge 2$. They proved this for $k=2$. In 2019, Glock proved this for $k=3$ and determined the limit. Quite recently, Glock, Joos, Kim, Kühn, Lichev and Pikhurko proved this for $k=4$ and determined the limit; we combine their work with a new reduction to fully resolve the conjecture by proving that indeed the limit exists for all positive integers $k\ge 2$.

arXiv comment10 pages, to appear in Proceedings of the AMS