# Chromatic Turán problems and a new upper bound for the Turán density of $\mathcal{K}_4^-$

Abstract : We consider a new type of extremal hypergraph problem: given an $r$-graph $\mathcal{F}$ and an integer $k≥2$ determine the maximum number of edges in an $\mathcal{F}$-free, $k$-colourable $r$-graph on $n$ vertices. Our motivation for studying such problems is that it allows us to give a new upper bound for an old problem due to Turán. We show that a 3-graph in which any four vertices span at most two edges has density less than $\frac{33}{ 100}$, improving previous bounds of $\frac{1}{ 3}$ due to de Caen [1], and $\frac{1}{ 3}-4.5305×10^-6$ due to Mubayi [9].
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Cited literature [12 references]

https://hal.inria.fr/hal-01184394
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### Citation

John Talbot. Chromatic Turán problems and a new upper bound for the Turán density of $\mathcal{K}_4^-$. 2005 European Conference on Combinatorics, Graph Theory and Applications (EuroComb '05), 2005, Berlin, Germany. pp.77-80, ⟨10.46298/dmtcs.3437⟩. ⟨hal-01184394⟩

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