EDB — 0MH

[0MH] Prerequisites:[0KS]↺↻. If \((X,𝜏)\) satisfies the second axiom of countability, given \(A⊆ X\) there exists a countable subset \(B⊆ A\) such that \(\overline B⊇ A\). In particular, the whole space \(X\) admits a dense countable subset: \(X\) is said to be separable. The vice versa holds for example in metric spaces, see [0Q7]↺↻. See also [0SQ]↺↻ for an application in \(ℝ^ n\).