EXTENDING CONCEPTUAL COMPLETENESS VIA VIRTUAL ULTRACATEGORIES

Abstract

Abstract We introduce the notion of virtual ultracategory. From a topological point of view, this notion can be seen as a categorification of relational β $\beta $ beta -modules. From a categorical point of view, virtual ultracategories generalize ultracategories in the same way that multicategories generalize monoidal categories. From a logical point of view, whereas the points of a coherent topos form an ultracategory, the points of an arbitrary topos form a virtual ultracategory. We then extend Makkai–Lurie’s conceptual completeness: a topos with enough points can be reconstructed from its virtual ultracategory of points.