In notation

In math­e­mat­ics, the no­ta­tion \(x \in X\) (where \(\in\) is writ­ten “\in” in LaTeX) means that \(X\) is a set and \(x\) is an el­e­ment of that set.

Examples

\(r \in \mathbb{R}\) means that \(r\) is a real num­ber.

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