General spectral supersaturation conjecture for friendship graphs

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For an integer k≥1k\geq 1, define

f(k)={k2−k,if k is odd;k2−32k,if k is even.f(k)= \begin{cases} k^2-k,&\text{if }k\text{ is odd};\\ k^2-\frac{3}{2}k,&\text{if }k\text{ is even}. \end{cases}

Let FkF_k be the friendship graph and let τk(G)\tau_k(G) denote the number of copies of FkF_k in GG. Let Ks,tqK_{s,t}^{q} be obtained from Ks,tK_{s,t} by adding qq pairwise disjoint edges within the part of size ss. The general spectral supersaturation conjecture. For every k≥1k\geq 1, there exists an absolute constant δ>0\delta>0 such that, for any sufficiently large nn and f(k)+1≤q≤δnf(k)+1\leq q\leq\delta\sqrt n, if GG is an nn-vertex graph satisfying

λ(G)≥λ(K⌈n2⌉,⌊n2⌋q),\lambda(G)\geq\lambda\left(K_{\lceil\frac{n}{2}\rceil,\lfloor\frac{n}{2}\rfloor}^{q}\right),

then

τk(G)≥(qk)⌊n2⌋,\tau_k(G)\geq\binom{q}{k}\left\lfloor\frac{n}{2}\right\rfloor,

with equality if and only if G=K⌈n2⌉,⌊n2⌋qG=K_{\lceil\frac{n}{2}\rceil,\lfloor\frac{n}{2}\rfloor}^{q}. This is presented as a conjectural extension of known extremal results, and the supplied text gives no resolution.

References

Primary source

Longfei Fang, Yongtao Li and Huiqiu Lin, “More on spectral supersaturation for the bowtie”, arXiv:2601.04671 (2026).

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