Pairs of these things are subject to the Axiom of pairing, which in turn is subject to the Axiom schema of replacement. A commonly used set of axioms for handling these was developed by Abraham Fraenkel [FRANE-kul] and Ernst Zermelo. The quantity commonly thought of as their size is called cardinality. Name this unordered collections of elements that can be operated on by 
Pairs of these things are subject to the Axiom of pairing, which in turn is subject to the Axiom schema of replacement. A commonly used set of axioms for handling these was developed by Abraham Fraenkel [FRANE-kul] and Ernst Zermelo. The quantity commonly thought of as their size is called cardinality. Name this unordered collections of elements that can be operated on by union and intersection.
Pairs of these things are subject to the Axiom of pairing, which in turn is subject to the Axiom schema of replacement.
sets