Supersaturation of Tree Posets

Tao Jiang, Sean Longbrake, Sam Spiro, Liana Yepremyan

Published 2024-06-17Version 1

A well-known result of Bukh shows that if $P$ is a tree poset of height $k$, then any subset of the Boolean lattice $\mathcal{F}\subseteq \mathcal{B}_n$ of size at least $(k-1+\varepsilon){n\choose \lceil n/2\rceil}$ contains at least one copy of $P$. This was extended by Boehnlein and Jiang to induced copies. We strengthen both results by showing that for any integer $q\ge k$, any family $\mathcal{F}$ of size at least $(q-1+\varepsilon){n\choose \lceil n/2\rceil}$ contains on the order of as many induced copies of $P$ as is contained in the $q$ middle layers of the Boolean lattice. This answers a conjecture of Gerbner, Nagy, Patk\'os, and Vizer in a strong form for tree posets.