The figure of Woman recurs in Alain Badiou's mathematical ontology. Not only does he cast the indiscernible element of set theoretical forcing as (♀) in Being and Event, but he also analogizes the depiction of femininity within the opera Ariadne and Bluebeard with his theory of appearance in Logics of Worlds. There the rebellious Ariadne’s matrix of relationships with Bluebeard’s willingly-imprisoned wives constitutes an “absolutely heterogenous feminine ground” exterior to the “new feminine world” that her eventual escape opens up. How can the ground of appearance be absolutely heterogenous yet still feminine, recognizably the world of Woman? Badiou uses category theory to argue that a being’s appearance is only possible between a minimum—Alladine, who stays—and a maximum—Ariadne, who leaves. This paper takes up his theories of change and appearance as a vital, if problematic, avenue for thinking gender and sex transition as a properly ontological event.