What is the equivalence of definitions for completely regular spaces?

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SUMMARY

The discussion centers on the equivalence of two definitions of "completely regular" spaces in topology. The first definition states that a space S is completely regular if for every closed subset C of S and every point x in S-C, there exists a continuous function f from S to the interval I such that f(x)=0 and f(C)=1. The second definition asserts that for every point p in S and every open set U containing p, there exists a continuous function f from S to I such that f(p)=0 and f(x)=1 for all points x in S-U. The equivalence is established by recognizing that the complement of U serves as the closed subset C.

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I have seen two different definitions of "completely regular" (one in my class and online, and the other in my textbook). I am having trouble seeing how these definitions are equivalent.

A space S is said to be completely regular if for every closed subset C of S and every point x in S-C there is a continuous function from S to I such that
f(x)=0 and f(C)=1

A space S is said to be completely regular if for every point p of S and for every open set U containing p, there is a continuous function of S into I such that f(p)=0 and f(x)=1 for all points x in S-U.
 
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Let C be the complement of U?
 
Ohhhh

I feel stupid now

I was thinking about this late at night, I'm not usually this dense.
 
Last edited:

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