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
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
(1995-04-10)