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Let M, N be monoids, and PSh(M), Psh(N) their respective categories of right actions on sets. In this paper, we systematically investigate correspondences between properties of geometric morphisms PSh(M) --> PSh(N) and properties of the semigroup homomorphisms M --> N or flat-left-N-right-M-sets inducing them. More specifically, we consider properties of geometric morphisms featuring in factorization systems, namely: surjections, inclusions, localic morphisms, hyperconnected morphisms, terminal-connected morphisms, étale morphisms, pure morphisms and complete spreads. We end with an application of topos-theoretic Galois theory to the special case of toposes of the form PSh(M).
@article{TAC_2024_40_a3, author = {Jens Hemelaer and Morgan Rogers}, title = {Geometric morphisms between toposes of monoid actions: factorization systems}, journal = {Theory and applications of categories}, pages = {80--129}, publisher = {mathdoc}, volume = {40}, year = {2024}, language = {en}, url = {http://geodesic.mathdoc.fr/item/TAC_2024_40_a3/} }
TY - JOUR AU - Jens Hemelaer AU - Morgan Rogers TI - Geometric morphisms between toposes of monoid actions: factorization systems JO - Theory and applications of categories PY - 2024 SP - 80 EP - 129 VL - 40 PB - mathdoc UR - http://geodesic.mathdoc.fr/item/TAC_2024_40_a3/ LA - en ID - TAC_2024_40_a3 ER -
Jens Hemelaer; Morgan Rogers. Geometric morphisms between toposes of monoid actions: factorization systems. Theory and applications of categories, Bunge Festschrift, Tome 40 (2024), pp. 80-129. http://geodesic.mathdoc.fr/item/TAC_2024_40_a3/