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Sh(X) never has a generator (unless X has the indiscrete topology)#210

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ScriptRaccoon merged 2 commits into
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dschepler:sheaves-no-generator
May 28, 2026
Merged

Sh(X) never has a generator (unless X has the indiscrete topology)#210
ScriptRaccoon merged 2 commits into
ScriptRaccoon:mainfrom
dschepler:sheaves-no-generator

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@dschepler dschepler commented May 27, 2026

It turns out this only resolves the direct assignment plus not being finitary algebraic.


  • unknown (category, property)-pairs before this PR: 116
  • unknown (category, property)-pairs after this PR: 114

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ScriptRaccoon commented May 27, 2026

Maybe we should even assume that $X$ is sober (a space has the same category of sheaves as its soberification, right?).

If you agree, you can add this right away to the file. Then this weird "not indiscrete" assumption becomes redundant, I assume.

Comment thread databases/catdat/data/categories/Sh(X).yaml Outdated
Comment thread databases/catdat/data/categories/Sh(X).yaml Outdated
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The new lemma could potentially be used to rewrite the assignments for SetxSet (where $(1,0)$ and $(0,1)$ are each a subterminal object which is not initial or terminal) and for Sp (where I guess for any $n$ the functor assigning 1 for sets of cardinality $n$ and $\varnothing$ otherwise is an intermediate subterminal object). Not sure whether it's worth it for SetxSet (in fact, the proof is easier in general in any situation where the intersection of all intermediate subterminal objects is initial) but in the existing argument for Sp I do see echoes (or foreshadowing) of the general lemma's proof.

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Looks very good! Can you please squash your commits into one? Then I will merge.

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The new lemma could potentially be used to rewrite the assignments for SetxSet [...] and for Sp

Yes. But let's only add a sentence like "Alternatively, this follows from ..."

@dschepler dschepler force-pushed the sheaves-no-generator branch from f42fa7b to 315a822 Compare May 28, 2026 12:59
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Looks very good! Can you please squash your commits into one? Then I will merge.

Done.

@ScriptRaccoon ScriptRaccoon merged commit f776468 into ScriptRaccoon:main May 28, 2026
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@dschepler dschepler deleted the sheaves-no-generator branch May 28, 2026 17:51
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