Empty-intersection conjecture for copies of complete graphs above the Turán threshold

Let V1,V2,,Vk1V_1,V_2,\ldots,V_{k-1} be the vertex classes of the balanced Turán graph Tk1(n)T_{k-1}(n), with sizes satisfying n2V1Vk1n2\left\lceil\frac n2\right\rceil\geq |V_1|\geq\cdots\geq |V_{k-1}|\geq\left\lfloor\frac n2\right\rfloor and iVi=n\sum_i|V_i|=n. Let Tk1T_{k-1}^{\sqsubset} be obtained from Tk1(n)T_{k-1}(n) by adding an edge {x,y}\{x,y\} in V1V_1, adding an edge {u,v}\{u,v\} in V2V_2, and deleting the edge {u,x}\{u,x\}. Empty-intersection conjecture. If a graph on nn vertices has tk1(n)+1t_{k-1}(n)+1 edges and the copies of KkK_k have empty intersection, then the number of copies of KkK_k is at least the number in Tk1T_{k-1}^{\sqsubset}, namely

(V21)V3V4Vk1+(V11)V3V4Vk1=(V1+V22)V3V4Vk1.(|V_2|-1)|V_3|\cdot|V_4|\cdots|V_{k-1}|+(|V_1|-1)|V_3|\cdot|V_4|\cdots|V_{k-1}|=(|V_1|+|V_2|-2)|V_3|\cdot|V_4|\cdots|V_{k-1}|.

This would generalize the paper's theorem for triangles, but the source gives no resolution and presents it as an open problem.

Sources & referencesView supporting material

Primary source

Chuanqi Xiao and Gyula O. H. Katona, “The number of triangles is more when they have no common vertex”, arXiv:2003.04450 (2020).

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