General spectral supersaturation conjecture for friendship graphs

For an integer k1k\geq 1, define

f(k)={k2k,if k is odd;k232k,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 k1k\geq 1, there exists an absolute constant δ>0\delta>0 such that, for any sufficiently large nn and f(k)+1qδnf(k)+1\leq q\leq\delta\sqrt n, if GG is an nn-vertex graph satisfying

λ(G)λ(Kn2,n2q),\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=Kn2,n2qG=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.

Sources & referencesView supporting material

Primary source

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

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