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:material-circle-edit-outline: 约 54 个字

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We can also talk about the size of a set, or its cardinality, denoted by |A|,

Intersections and Unions

Complements: written as B − A or B\A

2 proof

iff -> if and only if

We use the notation := to indicate a definition. For example, q := 6 defines variable q as having value 6.