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Aug 17, 2017 at 18:37 comment added MTyson You could try to find a similar categorical description of the space $T$ with elements $\{x,y,z\}$ and nontrivial closed sets $\{x,y\}$, $\{y,z\}$, and $\{y\}$. Then maps $f:X\to T$ with $x$ and $z$ in the image indicate that $f^{-1}(\{x,y\})$ and $f^{-1}(\{y,z\})$ are proper closed subsets covering $X$.
Aug 17, 2017 at 2:54 comment added Tim Campion Martin Brandenburg points out that there's a "brute force" categorical characterization of the Sierpinski space. From there, you can talk about closed sets categorically and so also irreducibility. But somehow this is not terribly satisfying.
Aug 16, 2017 at 22:54 comment added David Roberts By the way, I wish I could +1 your user page, handy code and all.
Aug 16, 2017 at 22:50 comment added David Roberts Maybe in terms of the corresponding locale? Just a thought...
Aug 16, 2017 at 21:13 history asked Arrow CC BY-SA 3.0