Hello! Tomorrow we will meet at 10:30am in B107. BBB link: https://bbb.lipn.univ-paris13.fr/b/rog-vao-uwm-s2j Last week I gave an introduction to categorical semantics, explaining the standard way that formulas-in-context are interpreted as subobjects, allowing us to interpret "geometric formulas" in any (Grothendieck) topos, and hence define models of "geometric theories". This background can be found in much more detail in chapters D1.1-1.3 of Johnstone's Sketches of an Elephant, or Caramello's Theories, Sites, Toposes. Let me know if you want access to a copy of either of those. This week, Jonas will pick up where I left off, with the aim of explaining what a classifying topos is. I will remember to record this session! See you there, Morgan