{"id":3163,"date":"2026-06-24T16:48:58","date_gmt":"2026-06-24T13:48:58","guid":{"rendered":"https:\/\/mathematics.haifa.ac.il\/?p=3163"},"modified":"2026-06-24T16:48:58","modified_gmt":"2026-06-24T13:48:58","slug":"u-haifa-topology-geometry-seminar-wednesday-june-24-2026-1300-speaker-emmanuel-farjoun-hebrew-university-title-impossible-functors-impossible-natural-transformations","status":"publish","type":"post","link":"https:\/\/mathematics.haifa.ac.il\/?p=3163","title":{"rendered":"U. Haifa Topology &amp; Geometry seminar: Wednesday, June 24, 2026, 13:00. Speaker: Emmanuel Farjoun (Hebrew University). Title: &#8220;Impossible functors, impossible natural transformations&#8221;."},"content":{"rendered":"\n<p class=\"wp-block-paragraph\">Let us start with two very believable observations:<br><br>1. The only functors from the category of all sets to that of finite sets are the constant ones.<br>2. Groups have no natural abelian subgroups.<br>We raise questions about infinite categorical and space analogs of these simple observations. We will try to put these facts into a wider context of augmented and co-augmented functors. The talk will mostly present open questions regarding the non-existence of functors and triviality of natural transformation between well-known functors.<br><br>Joint work with Sergei Ivanov and collaborators.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Recording:<br><a href=\"https:\/\/us02web.zoom.us\/rec\/share\/Zfxbz0-_pix1ClkJ2naZCQ-_beyB005CKSWCZuSwsosVVszQe-EqweXJJN4GPvQk.XJ_1HfPPCOoUshCi\">https:\/\/us02web.zoom.us\/rec\/share\/Zfxbz0-_pix1ClkJ2naZCQ-_beyB005CKSWCZuSwsosVVszQe-EqweXJJN4GPvQk.XJ_1HfPPCOoUshCi<\/a><\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><\/p>\n","protected":false},"excerpt":{"rendered":"<p>Let us start with two very believable observations: 1. The only functors from the category of all sets to that of finite sets are the constant ones.2. Groups have no natural abelian subgroups.We raise questions about infinite categorical and space&#8230;<br \/><a class=\"read-more-button\" href=\"https:\/\/mathematics.haifa.ac.il\/?p=3163\">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":[6,9,4],"tags":[],"class_list":["post-3163","post","type-post","status-publish","format-standard","hentry","category-gt-seminar","category-news","category-seminar"],"_links":{"self":[{"href":"https:\/\/mathematics.haifa.ac.il\/index.php?rest_route=\/wp\/v2\/posts\/3163","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=3163"}],"version-history":[{"count":1,"href":"https:\/\/mathematics.haifa.ac.il\/index.php?rest_route=\/wp\/v2\/posts\/3163\/revisions"}],"predecessor-version":[{"id":3164,"href":"https:\/\/mathematics.haifa.ac.il\/index.php?rest_route=\/wp\/v2\/posts\/3163\/revisions\/3164"}],"wp:attachment":[{"href":"https:\/\/mathematics.haifa.ac.il\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=3163"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/mathematics.haifa.ac.il\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=3163"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/mathematics.haifa.ac.il\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=3163"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}