Material set theory

Elementhood Relation Class Axiom

The Elementhood Relation Class Axiom is a possible axiom of material set theory with classes: #m/def/set/nbg

which is to say, there exists a Class, unique by extensionality, representing elementhood as a Relation class.¹ It is necessary to fix a construction of the ordered pair within the theory.

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