Subset Product within Semigroup is Associative

Theorem
Let $$\left({S, \circ}\right)$$ be a groupoid.

If $$\circ$$ is associative, then the operation $\circ_{\mathcal {P}}$ induced on the power set of $$S$$ is also associative.

Proof
Let $$\left({S, \circ}\right)$$ be a groupoid in which $$\circ$$ is associative.

Let $$X, Y, Z \in \mathcal {P} \left({S}\right)$$.

Then:


 * $$X \circ_{\mathcal {P}} \left({Y \circ_{\mathcal {P}} Z}\right) = \left\{{x \circ \left({y \circ z}\right): x \in X, y \in Y, z \in Z}\right\}$$


 * $$\left({X \circ_{\mathcal {P}} Y}\right) \circ_{\mathcal {P}} Z = \left\{{\left({x \circ y}\right) \circ z: x \in X, y \in Y, z \in Z}\right\}$$

... from which follows that $$\circ_{\mathcal {P}}$$ is associative on $$\mathcal {P} \left({S}\right)$$.