We give several reformulations of action accessibility in the sense of D. Bourn and G. Janelidze. In particular we prove that a pointed exact protomodular category is action accessible if and only if for each normal monomorphism $\kappa:X\to A$ the normalizer of $< \kappa,\kappa>: X\to A\times A$ exists. This clarifies the connection between normalizers and action accessible categories established in a joint paper of D. Bourn and the author, in which it is proved that for pointed exact protomodular categories the existence of normalizers implies action accessibility. In addition we prove a pointed exact protomodular category with coequalizers is action accessible if centralizers of normal monomorphisms exist, and the normality of unions holds.
Keywords: action accessible, protomodular, Barr exact, normality, centrality, normalizer, centralizer
@article{TAC_2015_30_a11,
author = {J. R. A. Gray},
title = {Normalizers, centralizers and action accessibility},
journal = {Theory and applications of categories},
pages = {410--432},
year = {2015},
volume = {30},
language = {en},
url = {http://geodesic.mathdoc.fr/item/TAC_2015_30_a11/}
}
J. R. A. Gray. Normalizers, centralizers and action accessibility. Theory and applications of categories, Tome 30 (2015), pp. 410-432. http://geodesic.mathdoc.fr/item/TAC_2015_30_a11/