Power Set and Two-Valued Functions are Isomorphic Boolean Rings

Theorem
Let $S$ be a set and let $\mathbf 2$ be the Boolean ring two.

Let $\mathcal P \left({S}\right)$ be the power set of $S$; by Power Set is Boolean Ring, it is a Boolean ring.

Let $\mathbf 2^S$ be the set of all mappings $f: S \to \mathbf 2$; by Two-Valued Functions form Boolean Ring, it is also a Boolean ring.

Let $\chi_{(\cdot)}: \mathcal P \left({S}\right) \to \mathbf 2^S$ be the characteristic function operation.

Then $\chi_{(\cdot)}$ is a ring isomorphism.

Proof
From Support Operation Inverse to Characteristic Function Operation, $\chi_{(\cdot)}$ is a bijection.

It therefore suffices to establish it is a ring homomorphism.

By Characteristic Function of Symmetric Difference:


 * $\chi_{A * B} = \chi_A + \chi_B - 2 \chi_A \chi_B$

Since $\mathbf 2^S$ is a Boolean ring, by Idempotent Ring has Characteristic Two, the right-hand side reduces to:


 * $\chi_{A * B} = \chi_A + \chi_B$

showing that $\chi_{(\cdot)}$ preserves ring addition.

By Characteristic Function of Intersection: Variant 1:


 * $\chi_{A \cap B} = \chi_A \cdot \chi_B$

showing that $\chi_{(\cdot)}$ preserves the ring product.

Hence $\chi_{(\cdot)}$ is a ring homomorphism.

The result follows.