And now a few relevant excerpts from the book:
"Unlike an ontological realist who would assert that numbers exist as ideal entities independently of the mind that thinks them, Badiou's thought is aligned with mathematical formalism.... Being does not derive from thought.... There must be a point of departure where being is posited. And this point is not, as some may imagine, the number one, but rather zero.... A mathematical thought of being, apart from its instantiation in symbols and manipulations, is nothing independently of these symbols and manipulations. And this nothing that is deemed to exist outside mathematical formulation is rudimentary for ontology as a whole. Zero exists.... Badious's thesis is that ontology is a discourse of being; it pronounces what is expressible of being" (46-7).