Let X be a topological space; let A be a subset of X. Suppose hat for each x ∈ A there is an open set U containing U ⊂ A. Show that A is open in X.

Elements Of Modern Algebra
8th Edition
ISBN:9781285463230
Author:Gilbert, Linda, Jimmie
Publisher:Gilbert, Linda, Jimmie
Chapter1: Fundamentals
Section1.2: Mappings
Problem 7TFE: Label each of the following statements as either true or false. A mapping is onto if and only if its...
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Let be a topological space; let be a subset of X. Suppose hat for each x ∈ there is an open set containing

U ⊂ A. Show that is open in X.

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