Material set theory

Complement Axiom for classes

The Complement Axiom is a possible axiom of Material set theory with classes¹: #m/def/set/nbg

which is to say, the complement of a class 𝑋 (within the universe of everything except proper classes) exists, which by extensionality is unique and we denote the 𝑋𝑐. It follows immediately that we have a universal class

#state/tidy | #lang/en | #SemBr