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arXiv · 1805.06767

Model theory of Steiner triple systems

Silvia Barbina·Enrique Casanovas
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Abstract

A Steiner triple system is a set $S$ together with a collection $\mathcal{B}$ of subsets of $S$ of size 3 such that any two elements of $S$ belong to exactly one element of $\mathcal{B}$. It is well known that the class of finite Steiner triple systems has a Fra\"{\i}ss\'e limit $M_{\mathrm{F}}$. Here we show that the theory $T^\ast_\mathrm{Sq}$ of $M_{\mathrm{F}}$ is the model completion of the theory of Steiner triple systems. We also prove that $T^\ast_\mathrm{Sq}$ is not small and it has quantifier elimination, $\mathrm{TP}_2$, $\mathrm{NSOP}_1$, elimination of hyperimaginaries and weak elimination of imaginaries.

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Silvia Barbina, Enrique Casanovas. 2018-05-17. Model theory of Steiner triple systems. https://doi.org/10.1142/s0219061320500105

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