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Let $(X,\tau)$ be a compactly generated Hausdorff space, that is, a set $F\subset X$ is closed if and only if the intersection of $F$ with every compact set is closed.

Further let $\mathcal F$ be a family of continuous functions separating points from compact sets, that is, such that for every $x\in X$ and every compact $K$ there exists $f\in\mathcal F$ and $a=a_{x,K}>0$ with $f(x)=0$ and $f\geq a$ on $K$.

Question: Is it true that $\mathcal F$ generates $\tau$?

Comments:

  1. The statement above is supposed to mimick the analogous one for closed sets (in place of compact sets):

If $\mathcal F$ is a family of continuous functions separating points from closed sets, then $\mathcal F$ generates $\tau$

a proof of which can be found here.

  1. The reason for assuming Hausdorffness is that (otherwise) there are many (in)equivalent definitions of compactly generated topological space (see here).

  2. If necessary, I am happy to assume that $(X,\tau)$ is completely regular, so that $\mathcal F$ is known a priori to be generated by the family of all continuous functions.

AlephBeth
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  • How about taking $X$ to be an infinite discrete space? According to your requirements we can let $\mathcal{F}$ be the collection of characteristic functions of finite subsets of $X$. The topology this family generate is not even Hausdorff. – Tyrone Feb 28 '23 at 08:44
  • @Tyrone indeed that's a very good point, thank you. I would be interested in sufficient conditions for the statement to be true, but you could post your comment as a negative answer if you like. – AlephBeth Mar 01 '23 at 10:11

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