Let A be a set of real numbers. We say that A is an open set...

Let A be a set of real numbers. We say that A is an open set if for every x₀ ∈ A there is some δ > 0 (which might depend on x₀) such that (x₀ − δ, x₀ + δ) ⊆ A. Show that a set B of real numbers is closed if and only if B is the complement of some open set A

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Colby Messinger answered 1 year ago

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