{"id":3061,"date":"2025-11-19T18:39:46","date_gmt":"2025-11-19T16:39:46","guid":{"rendered":"https:\/\/mathematics.haifa.ac.il\/?p=3061"},"modified":"2025-11-26T12:09:08","modified_gmt":"2025-11-26T10:09:08","slug":"u-haifa-topology-geometry-seminar-wednesday-november-19-2025-speaker-fernando-abellan-max-planck-title-%e2%88%9e-2-topoi-and-descent","status":"publish","type":"post","link":"https:\/\/mathematics.haifa.ac.il\/?p=3061","title":{"rendered":"U. Haifa Topology &amp; Geometry seminar: Wednesday, November 19, 2025. Speaker: Fernando Abellan (Max Planck). Title: &#8220;(\u221e, 2)-Topoi and Descent&#8221;."},"content":{"rendered":"\n<p class=\"wp-block-paragraph\">The goal of this talk is to introduce the notion of a Grothendieck (\u221e, 2)-topos as a presentable (\u221e, 2)-category satisfying a categorified version of the descent axiom for (\u221e, 1)- topoi of Rezk-Lurie, which we call fibrational descent.As the name indicates, fibrational descent axiomatizes the structure of internal fibrations in an (\u221e, 2)-category and it is closely related to the straightening-unstraightening equivalence of Grothendieck-Lurie. After presenting the main definition, I will give an overview of several different ways of characterising 2-topoi, which includes a 2-dimensional version of Giraud\u2019s theorem and categorified Lawvere-Tierney axioms. Moreover, I will show how the theory of internal categories in an (\u221e, 1)-topos (as develop by Martini and Wolf) can be embedded into our formalism as (\u221e, 1)-localic 2-topoi. If time permits, I will explain how to construct a version of the Yoneda embedding in an (\u221e, 2)-topos and a theory of partially lax Kan extensions.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Recoding:<br><a href=\"https:\/\/us02web.zoom.us\/rec\/share\/T2xs7unRA9fvIskhL7vvdPLN0RXZ4HMlSGRLTpH30KODuP-ovne-zjB92ggPMU9I.02CP7rLBeEc3qSAe\">https:\/\/us02web.zoom.us\/rec\/share\/T2xs7unRA9fvIskhL7vvdPLN0RXZ4HMlSGRLTpH30KODuP-ovne-zjB92ggPMU9I.02CP7rLBeEc3qSAe<\/a><\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><br><\/p>\n","protected":false},"excerpt":{"rendered":"<p>The goal of this talk is to introduce the notion of a Grothendieck (\u221e, 2)-topos as a presentable (\u221e, 2)-category satisfying a categorified version of the descent axiom for (\u221e, 1)- topoi of Rezk-Lurie, which we call fibrational descent.As the&#8230;<br \/><a class=\"read-more-button\" href=\"https:\/\/mathematics.haifa.ac.il\/?p=3061\">Read more<\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[6,4],"tags":[],"class_list":["post-3061","post","type-post","status-publish","format-standard","hentry","category-gt-seminar","category-seminar"],"_links":{"self":[{"href":"https:\/\/mathematics.haifa.ac.il\/index.php?rest_route=\/wp\/v2\/posts\/3061","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/mathematics.haifa.ac.il\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/mathematics.haifa.ac.il\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/mathematics.haifa.ac.il\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/mathematics.haifa.ac.il\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=3061"}],"version-history":[{"count":1,"href":"https:\/\/mathematics.haifa.ac.il\/index.php?rest_route=\/wp\/v2\/posts\/3061\/revisions"}],"predecessor-version":[{"id":3062,"href":"https:\/\/mathematics.haifa.ac.il\/index.php?rest_route=\/wp\/v2\/posts\/3061\/revisions\/3062"}],"wp:attachment":[{"href":"https:\/\/mathematics.haifa.ac.il\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=3061"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/mathematics.haifa.ac.il\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=3061"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/mathematics.haifa.ac.il\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=3061"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}