Set Difference Union Intersection/Proof 1

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Theorem

$S = \paren {S \setminus T} \cup \paren {S \cap T}$


Proof

\(\ds \paren {S \setminus T} \cup \paren {S \cap T}\) \(=\) \(\ds \paren {\paren {S \setminus T} \cup S} \cap \paren {\paren {S \setminus T} \cup T}\) Union Distributes over Intersection
\(\ds \) \(=\) \(\ds S \cap \paren {\paren {S \setminus T} \cup T}\) Set Difference Union First Set is First Set
\(\ds \) \(=\) \(\ds S \cap \paren {S \cup T}\) Set Difference Union Second Set is Union
\(\ds \) \(=\) \(\ds S\) Intersection Absorbs Union

$\blacksquare$