Mubayi–Zhao conjecture for forbidden traces of complete uniform hypergraphs

Let Ks(t)K_s^{(t)} be the complete ss-vertex tt-uniform hypergraph. Let Trr(Ks(t))\operatorname{Tr}_r(K_s^{(t)}) be the family of all rr-uniform induced Berge copies of Ks(t)K_s^{(t)}, and let Ht,srH_{t,s}^r be the member with the maximum number of vertices, obtained by adding rtr-t new vertices to each edge of Ks(t)K_s^{(t)}, with each new vertex used by only one edge.

Mubayi–Zhao conjecture. Given positive integers n,r,s,tn,r,s,t with 2t<min{r,s}2\leqslant t<\min\{r,s\}, there exists n0>0n_0>0 such that for n>n0n>n_0,

ex(n,Trr(Ks(t)))={ex(n,Ht,sr)if r<s,ex(nr+s1,Trs1(Ks(t)))=ex(nr+s1,Ht,ss1)if rs.\operatorname{ex}(n,\operatorname{Tr}_r(K_s^{(t)}))= \begin{cases} \operatorname{ex}(n,H_{t,s}^r) & \text{if }r<s,\\ \operatorname{ex}(n-r+s-1,\operatorname{Tr}_{s-1}(K_s^{(t)}))=\operatorname{ex}(n-r+s-1,H_{t,s}^{s-1}) & \text{if }r\geqslant s. \end{cases}

The stated formula would determine the asymptotic extremal number for forbidden induced Berge copies of complete uniform hypergraphs; the general case is presented as an open problem.

Sources & referencesView supporting material

Primary source

Mingze Li, Jie Ma and Mingyuan Rong, “Recent advances in arrow relations and traces of sets”, arXiv:2507.23375 (2025).

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