Powerset is not Subset of its Set/Proof 3
Let $A$ be a set.
- $\powerset A \not \subseteq A$
Aiming for a contradiction, suppose that $\powerset A \subseteq A$.
Since $A \in \powerset A$, this implies:
- $A \in A$
Axiom of Foundation
This theorem depends on the Axiom of Foundation.
Most mathematicians accept the Axiom of Foundation, but theories that reject it, or negate it, have found applications in Computer Science and Linguistics.