English

Accessible images revisited

Category Theory 2016-03-23 v2 Logic

Abstract

We extend and improve the result of Makkai and Par\'e that the powerful image of any accessible functor F is accessible, assuming there exists a sufficiently large strongly compact cardinal. We reduce the required large cardinal assumption to the existence of Lμ,ωL_{\mu,\omega}-compact cardinals for sufficiently large {\mu}, and also show that under this assumption the {\lambda}-pure powerful image of F is accessible. From the first of these statements, we obtain that the tameness of every Abstract Elementary Class follows from a weaker large cardinal assumption than was previously known. We provide two ways of employing the large cardinal assumption to prove each result - one by a direct ultraproduct construction and one using the machinery of elementary embeddings of the set-theoretic universe.

Keywords

Cite

@article{arxiv.1506.01986,
  title  = {Accessible images revisited},
  author = {Andrew Brooke-Taylor and Jiří Rosický},
  journal= {arXiv preprint arXiv:1506.01986},
  year   = {2016}
}

Comments

14 pages; amended after referee's comments, mostly to improve exposition. We have changed terminology for the large cardinal axiom - this is discussed in some depth after Definition 2.3

R2 v1 2026-06-22T09:48:08.402Z