The empty set (written [math]\href{/cs2800/wiki/index.php/%E2%88%85}{∅}
[/math] or [math]\href{/cs2800/wiki/index.php/Enumerated_set}{\{\}}
[/math]) is a set; [math]x \href{/cs2800/wiki/index.php/%5Cnotin}{\notin} \href{/cs2800/wiki/index.php/%E2%88%85}{∅}
[/math] for all [math]x
[/math].
