Set Difference with Set Difference is Union of Set Difference with Intersection

Theorem
Let $$R, S, T$$ be sets.

Then:
 * $$R \setminus \left({S \setminus T}\right) = \left({R \setminus S}\right) \cup \left({R \cap T}\right)$$

where:
 * $$S \setminus T$$ denotes set difference;
 * $$S \cup T$$ denotes set union;
 * $$S \cap T$$ denotes set intersection.

Proof
Consider $$R, S, T \subseteq \mathbb U$$, where $$\mathbb U$$ is considered as the universe.

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