Positively closed $Sh(B)$-valued models
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 -valued models of coherent theories they coincide. We prove that if for a complete Boolean algebra, then positively closed but not strongly positively closed -valued models of coherent theories exist, yet, there is an alternative local property which characterizes positively closed -valued models. A large part of our discussion is given in the context of infinite quantifier geometric logic, dealing with the fragment where is weakly compact.
Cite
@article{arxiv.2409.11231,
title = {Positively closed $Sh(B)$-valued models},
author = {Kristóf Kanalas},
journal= {arXiv preprint arXiv:2409.11231},
year = {2026}
}