Zermelo Frankel set theory

mathematics A set theory with the axioms of Zermelo settheory (Extensionality, Union, Pair-set, Foundation,

Restriction, Infinity, Power-set) plus the Replacement axiomschema:

If F(x,y) is a formula such that for any x, there is a

unique y making F true, and X is a set, then

F x : x in X

is a set. In other words, if you do something to each element

of a set, the result is a set.

An important but controversial axiom which is NOT part of ZF

theory is the Axiom of Choice.

(1995-04-10)