# 元素 (數學)

## 集合

${\displaystyle A=\{1,2,3,4\}}$ 表示集合${\displaystyle A}$ 中有四个元素，分别是数字1、2、3、4。由集合${\displaystyle A}$ 中元素组成的集合是${\displaystyle A}$ 子集，例如 ${\displaystyle \{1,2\}}$

## 符号和术语

${\displaystyle x\in A}$

${\displaystyle A\ni x}$

${\displaystyle x\notin A}$

Signum ∈ significat est. Ita a ∈ b legitur a est quoddam b; …

Unicode名称 Element of Not an element of Contains as member Does not contain as member

Unicode 8712 U+2208 8713 U+2209 8715 U+220B 8716 U+220C
UTF-8 226 136 136 E2 88 88 226 136 137 E2 88 89 226 136 139 E2 88 8B 226 136 140 E2 88 8C

LaTeX \in \notin \ni \not\ni or \notni
Wolfram Mathematica \[Element] \[NotElement] \[ReverseElement] \[NotReverseElement]

## 注释

1. ^ 这里的“X”是希腊数字的10

## 參考資料

1. ^ Eric Schechter. Handbook of Analysis and Its Foundations. Academic Press. 1997. ISBN 0-12-622760-8. p. 12
2. ^ George Boolos. 24.243 Classical Set Theory (lecture) (演讲). 麻省理工学院. February 4, 1992.
3. Kennedy, H. C. What Russell learned from Peano. Notre Dame Journal of Formal Logic (Duke University Press). July 1973, 14 (3): 367–372. MR 0319684. .