Tietze extension theorem

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What Wikipedia says

In topology, the Tietze extension theorem (also known as the Tietze–Urysohn–Brouwer extension theorem or Urysohn-Brouwer lemma) states that any real-valued, continuous function on a closed subset of a normal topological space can be extended to the entire space, preserving boundedness if necessary.

Excerpt from the Wikipedia article “Tietze extension theorem”, under the CC BY-SA 4.0 license. Read the article on Wikipedia

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