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For any set $X$ and cardinal $\kappa$ let $[X]^\kappa$ be the collection of all subsets of $X$ of cardinality $\kappa$.

I was looking for $T_2$-spaces $(X,\tau)$ with the property that

$(P)$ there is an injective function $f:[X]^\omega\to \tau$ such that for all $s\in [X]^\omega$ we have $s\subseteq f(s)$.

Question. If $(X,\tau)$ is infinite, Hausdorff, and non-separable, is there a function with the properties described in $(P)$?

Note. I had the following remark in the original version of this post, but KP Hart made me aware that it is false - thanks for spotting my mistake!

[False] Obviously, if $(X,\tau)$ is separable and contains at least two different countable dense subsets $s$, $s'$, then the only member of $\tau$ that contains $s$ or $s'$ is $X$ itself, so there cannot be an injective function $f$ as described in $(P)$.

Question. If $(X,\tau)$ is infinite, Hausdorff, and non-separable, is there a function with the properties described in $(P)$? [/False]

For any set $X$ and cardinal $\kappa$ let $[X]^\kappa$ be the collection of all subsets of $X$ of cardinality $\kappa$.

I was looking for $T_2$-spaces $(X,\tau)$ with the property that

$(P)$ there is an injective function $f:[X]^\omega\to \tau$ such that for all $s\in [X]^\omega$ we have $s\subseteq f(s)$.

Obviously, if $(X,\tau)$ is separable and contains at least two different countable dense subsets $s$, $s'$, then the only member of $\tau$ that contains $s$ or $s'$ is $X$ itself, so there cannot be an injective function $f$ as described in $(P)$.

Question. If $(X,\tau)$ is infinite, Hausdorff, and non-separable, is there a function with the properties described in $(P)$?

For any set $X$ and cardinal $\kappa$ let $[X]^\kappa$ be the collection of all subsets of $X$ of cardinality $\kappa$.

I was looking for $T_2$-spaces $(X,\tau)$ with the property that

$(P)$ there is an injective function $f:[X]^\omega\to \tau$ such that for all $s\in [X]^\omega$ we have $s\subseteq f(s)$.

Question. If $(X,\tau)$ is infinite, Hausdorff, and non-separable, is there a function with the properties described in $(P)$?

Note. I had the following remark in the original version of this post, but KP Hart made me aware that it is false - thanks for spotting my mistake!

[False] Obviously, if $(X,\tau)$ is separable and contains at least two different countable dense subsets $s$, $s'$, then the only member of $\tau$ that contains $s$ or $s'$ is $X$ itself, so there cannot be an injective function $f$ as described in $(P)$. [/False]

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Injective choice function for non-separable $T_2$-spaces

For any set $X$ and cardinal $\kappa$ let $[X]^\kappa$ be the collection of all subsets of $X$ of cardinality $\kappa$.

I was looking for $T_2$-spaces $(X,\tau)$ with the property that

$(P)$ there is an injective function $f:[X]^\omega\to \tau$ such that for all $s\in [X]^\omega$ we have $s\subseteq f(s)$.

Obviously, if $(X,\tau)$ is separable and contains at least two different countable dense subsets $s$, $s'$, then the only member of $\tau$ that contains $s$ or $s'$ is $X$ itself, so there cannot be an injective function $f$ as described in $(P)$.

Question. If $(X,\tau)$ is infinite, Hausdorff, and non-separable, is there a function with the properties described in $(P)$?