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arXiv · 2001.06995

Nov\'{a}k's conjecture on cyclic Steiner triple systems and its generalization

Tao Feng·Daniel Horsley·Xiaomiao Wang
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Abstract

Nov\'{a}k conjectured in 1974 that for any cyclic Steiner triple systems of order $v$ with $v\equiv 1\pmod{6}$, it is always possible to choose one block from each block orbit so that the chosen blocks are pairwise disjoint. We consider the generalization of this conjecture to cyclic $(v,k,\lambda)$-designs with $1 \leq \lambda \leq k-1$. Superimposing multiple copies of a cyclic symmetric design shows that the generalization cannot hold for all $v$, but we conjecture that it holds whenever $v$ is sufficiently large compared to $k$. We confirm that the generalization of the conjecture holds when $v$ is prime and $\lambda=1$ and also when $\lambda \leq (k-1)/2$ and $v$ is sufficiently large compared to $k$. As a corollary, we show that for any $k \geq 3$, with the possible exception of finitely many composite orders $v$, every cyclic $(v,k,1)$-design without short orbits is generated by a $(v,k,1)$-disjoint difference family.

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Tao Feng, Daniel Horsley, Xiaomiao Wang. 2020-01-20. Nov\'{a}k's conjecture on cyclic Steiner triple systems and its generalization. https://doi.org/10.1016/j.jcta.2021.105515

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