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Stability in affine logic

Itaï Ben Yaacov and Tomás Ibarlucía

Vol. 5 (2026), No. 1, 1–34
Abstract

We develop foundational aspects of stability theory in affine logic. On the one hand, we prove appropriate affine versions of many classical results, including definability of types, existence of nonforking extensions, and other fundamental properties of forking calculus. Most notably, stationarity holds over arbitrary sets (in fact, every type is Lascar strong). On the other hand, we prove that stability is preserved under direct integrals of measurable fields of structures. We deduce that stability in the extremal models of an affine theory implies stability of the theory. We also deduce that the affine part of a stable continuous logic theory is affinely stable, generalising the result of preservation of stability under randomisations.

Keywords
affine logic, stability, continuous logic
Mathematical Subject Classification
Primary: 03C45, 03C66
Milestones
Received: 21 March 2025
Revised: 27 October 2025
Accepted: 18 December 2025
Published: 7 March 2026
Authors
Itaï Ben Yaacov
Institut Camille Jordan
Université Claude Bernard Lyon 1
Lyon
France
Tomás Ibarlucía
Université Paris Cité
CNRS
IMJ-PRG
F-75013 Paris
France