For any set theoretic formula 
,
 |
In other words, for any formula and set 
there is a subset of 
consisting exactly of those elements which satisfy the formula.
Axioms of Subsets
This entry contributed by Nicolas Bray
Explore with Wolfram|Alpha
Cite this as:
Bray, Nicolas. "Axioms of Subsets." From MathWorld--A Wolfram Web Resource, created by Eric W. Weisstein. https://mathworld.wolfram.com/AxiomsofSubsets.html