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DIVIDING LINES BETWEEN POSITIVE THEORIES

Published online by Cambridge University Press:  06 December 2023

ANNA DMITRIEVA
Affiliation:
SCHOOL OF MATHEMATICS, UNIVERSITY OF EAST ANGLIA, NORWICH, UK E-mail: a.dmitrieva@uea.ac.uk
FRANCESCO GALLINARO*
Affiliation:
MATHEMATISCHES INSTITUT, ALBERT-LUDWIGS-UNIVERSITÄT FREIBURG, FREIBURG, GERMANY URL: https://fgallinaro.github.io/
MARK KAMSMA
Affiliation:
DEPARTMENT OF MATHEMATICS, IMPERIAL COLLEGE LONDON, LONDON, UK E-mail: mark@markkamsma.nl URL: https://markkamsma.nl

Abstract

We generalise the properties $\mathsf {OP}$, $\mathsf {IP}$, k-$\mathsf {TP}$, $\mathsf {TP}_{1}$, k-$\mathsf {TP}_{2}$, $\mathsf {SOP}_{1}$, $\mathsf {SOP}_{2}$, and $\mathsf {SOP}_{3}$ to positive logic, and prove various implications and equivalences between them. We also provide a characterisation of stability in positive logic in analogy with the one in full first-order logic, both on the level of formulas and on the level of theories. For simple theories there are the classically equivalent definitions of not having $\mathsf {TP}$ and dividing having local character, which we prove to be equivalent in positive logic as well. Finally, we show that a thick theory T has $\mathsf {OP}$ iff it has $\mathsf {IP}$ or $\mathsf {SOP}_{1}$ and that T has $\mathsf {TP}$ iff it has $\mathsf {SOP}_{1}$ or $\mathsf {TP}_{2}$, analogous to the well-known results in full first-order logic where $\mathsf {SOP}_{1}$ is replaced by $\mathsf {SOP}$ in the former and by $\mathsf {TP}_{1}$ in the latter. Our proofs of these final two theorems are new and make use of Kim-independence.

Type
Article
Copyright
© The Author(s), 2023. Published by Cambridge University Press on behalf of The Association for Symbolic Logic

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