English

Categoricity and Universal Classes

Logic 2018-01-10 v2

Abstract

Let (K,)(\mathcal{K} ,\subseteq ) be a universal class with LS(K)=λLS(\mathcal{K})=\lambda categorical in regular κ>λ+\kappa >\lambda^+ with arbitrarily large models, and let K\mathcal{K}^* be the class of all AK>λ\mathcal{A}\in\mathcal{K}_{>\lambda} for which there is BKκ\mathcal{B} \in \mathcal{K}_{\ge\kappa} such that AB\mathcal{A}\subseteq\mathcal{B}. We prove that K\mathcal{K}^* is categorical in every ξ>λ+\xi >\lambda^+, K(2λ+)+K\mathcal{K}_{\ge\beth_{(2^{\lambda^+})^+}} \subseteq \mathcal{K}^{*}, and the models of K>λ+\mathcal{K}^*_{>\lambda^+} are essentially vector spaces (or trivial i.e. disintegrated).

Keywords

Cite

@article{arxiv.1712.08532,
  title  = {Categoricity and Universal Classes},
  author = {Tapani Hyttinen and Kaisa Kangas},
  journal= {arXiv preprint arXiv:1712.08532},
  year   = {2018}
}
R2 v1 2026-06-22T23:27:33.160Z