Bradač–Janzer–Sudakov–Tomon conjecture for Cartesian products of trees

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For graphs FF and GG, their Cartesian product F□GF\Box G has vertex set V(F)×V(G)V(F)\times V(G), with (u,v)(u,v) adjacent to (u′,v′)(u',v') if and only if either u=u′u=u' and vv′∈E(G)vv'\in E(G), or v=v′v=v' and uu′∈E(F)uu'\in E(F). Let TT and SS be trees, each with at least one edge. Bradač–Janzer–Sudakov–Tomon conjecture. There exist positive real numbers cc and CC such that

cn3/2≤ex(n,T□S)≤Cn3/2.cn^{3/2}\leq \mathrm{ex}(n,T\Box S)\leq Cn^{3/2}.

This extends the proved order of magnitude for the Cartesian product of a nontrivial tree and a nontrivial path. The conjecture remains open in general.

References

Primary source

Lanchao Wang and Caihong Yang, “The Turán number of the Cartesian product of trees via star-flip”, arXiv:2607.28295 (2026).

Additional references

2 papers in this index state this conjecture (2023–2026). The statement above is taken from the most recent of them; the others are arXiv:2302.03278.

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