During the proof of Lemma 39.1. of the Munkres' Topology, it is written "In general $\bigcup \bar A \subset \bar {\bigcup A}$." But it is not so obvious to me to prove it.
Simple detailed explanation would be much appreciated.
On the Lemma 39.1. of the Munkres' Topology
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$\begingroup$
general-topology
proof-explanation
1 Answers
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I only want to give a hint: From $A\subseteq\bigcup A$, we deduce that $\bar A\subseteq \overline{\bigcup A}$.
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0İ cant believe how easy it was.. Thank you. – 2017-02-01