اجتماع (نظریه مجموعه‌ها)

${\displaystyle \bigcup S:=\bigcup _{A\in S}A:=\{x\in C:\exists A\in S,x\in A\}}$

${\displaystyle A_{1}\cup A_{2}\cup \cdots \cup A_{n}=(A_{1}\cup A_{2}\cup \cdots \cup A_{n-1})\cup A_{n}}$

${\displaystyle A\cup A=A}$

${\displaystyle A\cup B=B\cup A}$

${\displaystyle A\cup \phi =\phi \cup A=A}$

${\displaystyle (A\cup B)\cup C=A\cup (B\cup C)}$

${\displaystyle A\cup (B\cap C)=(A\cup B)\cap (A\cup C)}$

${\displaystyle A\cap (B\cup C)=(A\cap B)\cup (A\cap C)}$