De Morgan's Laws (Set Theory)/Set Difference/Difference with Intersection/Corollary
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Corollary to De Morgan's Laws: Difference with Intersection
Let $S, T_1, T_2$ be sets.
Suppose that $T_1 \subseteq S$.
Then:
- $S \setminus \paren {T_1 \cap T_2} = \paren {S \setminus T_1} \cup \paren {T_1 \setminus T_2}$
Proof
\(\ds S \setminus \paren {T_1 \cap T_2}\) | \(=\) | \(\ds \paren {S \setminus T_1} \cup \paren {S \setminus T_2}\) | De Morgan's Laws: Difference with Intersection | |||||||||||
\(\ds \) | \(=\) | \(\ds \paren {S \setminus T_1} \cup \paren {\paren {\paren {S \setminus T_1} \cup \paren {S \cap T_1} } \setminus T_2}\) | Set Difference Union Intersection | |||||||||||
\(\ds \) | \(=\) | \(\ds \paren {S \setminus T_1} \cup \paren {\paren {S \setminus T_1} \setminus T_2} \cup \paren {\paren {S \cap T_1} \setminus T_2}\) | Set Difference is Right Distributive over Union | |||||||||||
\(\ds \) | \(=\) | \(\ds \paren {S \setminus T_1} \cup \paren {\paren {S \setminus T_1} \setminus T_2} \cup \paren {T_1 \setminus T_2}\) | Intersection with Subset is Subset: $T_1 \subseteq S$ | |||||||||||
\(\ds \) | \(=\) | \(\ds \paren {S \setminus T_1} \cup \paren {T_1 \setminus T_2}\) | Set Difference Union First Set is First Set |
$\blacksquare$