Set

Abstract

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$$\{9,8,7\}=\{7,9,8\}=\{7,8,7,9,9,7,7\}$$

• A unordered collection of elements, so the order and duplicates don’t matter

Set Elements

• Example: 1, 2, 3 {1} are objects in the set of Integer (整数)
• It can be either a value or a set

Membership of a Set

$$\in ,\notin$$ $$b\in a,b,c$$

Cardinality of a Set

$$|\{a,b,c\}|=3$$

• The size of the Set