Skip to main content
2 of 2
added 4 characters in body
Joel David Hamkins
  • 236.3k
  • 44
  • 777
  • 1.4k

The answer is no. Consider the space $X=\{0,1,2\}$ with the topology $\tau=\{\emptyset,\{0\},\{1,2\},X\}$. There are precisely two injective neighborhood selectors, both of which are almost surjective in your sense. Namely, we must map $0\mapsto\{0\}$ and then $1$ and $2$ get mapped to $\{1,2\}$ and $X$, in either way.

So this space is critical in your sense, but the topology is not of your form $\tau_\alpha$ for any ordinal $\alpha$. For example, it is not $T_0$, since we cannot separate $1$ and $2$.

Joel David Hamkins
  • 236.3k
  • 44
  • 777
  • 1.4k