I bought a maths book and have discovered it's somewhat above my level.(adsbygoogle = window.adsbygoogle || []).push({});

In particular I'm confused about one bit of notation. I understand the "is a member of" operator when it takes a set as argument (e.g. n ∈ ℝ) but not when the book uses it with functions (e.g. n ∈ f)

Does n ∈ f mean that the number n can be returned by function f?

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# I Help with set theory notation

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