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.

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.

*This entry contributed by Nicolas
Bray*

Bray, Nicolas. "Axioms of Subsets." From *MathWorld*--A Wolfram Web Resource, created by Eric
W. Weisstein. https://mathworld.wolfram.com/AxiomsofSubsets.html