Vector-space Erdős Matching Conjecture

Let VV be an nn-dimensional vector space over Fq\mathbb{F}_q, and let mq(n,k,s)m_q(n,k,s) be the maximum size of a family F[Vk]\mathcal{F}\subseteq\genfrac{[}{]}{0pt}{}{V}{k} containing no s+1s+1 members whose sum is direct; equivalently, if νq(F)\nu_q(\mathcal{F}) is the largest integer ss for which some F1,,FsFF_1,\ldots,F_s\in\mathcal{F} satisfy dim(F1++Fs)=sk\dim(F_1+\cdots+F_s)=sk, then νq(F)s\nu_q(\mathcal{F})\le s. Vector-space Erdős Matching Conjecture. For all n(s+1)kn\ge (s+1)k,

mq(n,k,s)=max{[(s+1)k1k]q, [nk]qqsk[nsk]q}.m_q(n,k,s)=\max\left\{\genfrac{[}{]}{0pt}{}{(s+1)k-1}{k}_q,~\genfrac{[}{]}{0pt}{}{n}{k}_q-q^{sk}\genfrac{[}{]}{0pt}{}{n-s}{k}_q\right\}.

The two terms are attained by the families of kk-subspaces contained in a fixed ((s+1)k1)((s+1)k-1)-subspace and of kk-subspaces meeting a fixed ss-subspace nontrivially, respectively. This is the vector-space analogue of the Erdős Matching Conjecture and connects extremal matching problems with matroid theory, coding theory, and cover-free families. The source does not state a resolution in general.

Sources & referencesView supporting material

Primary source

Baoyan Feng, Chong Shangguan, Yulin Yang and Chenyang Zhang, “An Erdős Matching Conjecture for Vector Spaces”, arXiv:2606.24529 (2026).

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