English

Positively closed $Sh(B)$-valued models

Category Theory 2026-02-02 v3 Logic

Abstract

We study positively closed and strongly positively closed topos-valued models of coherent theories. Positively closed is a global notion (it is defined in terms of all possible outgoing homomorphisms), while strongly positively closed is a local notion (it only concerns the definable sets inside the model). For Set\mathbf{Set}-valued models of coherent theories they coincide. We prove that if E=Sh(B,τcoh)\mathcal{E}=Sh(B,\tau _{coh}) for a complete Boolean algebra, then positively closed but not strongly positively closed E\mathcal{E}-valued models of coherent theories exist, yet, there is an alternative local property which characterizes positively closed E\mathcal{E}-valued models. A large part of our discussion is given in the context of infinite quantifier geometric logic, dealing with the fragment LκκgL^g_{\kappa \kappa } where κ\kappa is weakly compact.

Keywords

Cite

@article{arxiv.2409.11231,
  title  = {Positively closed $Sh(B)$-valued models},
  author = {Kristóf Kanalas},
  journal= {arXiv preprint arXiv:2409.11231},
  year   = {2026}
}
R2 v1 2026-06-28T18:47:53.317Z