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The paper Étale cohomology of diamonds defines partial properness and compactification for maps between v-sheaves, and in particular for perfectoid spaces and rigid-analytic spaces. Recently when reading Lectures on Analytic Geometry I found that there may be similar concepts for analytic spaces. Here's my attempting definition (I still prefer the notation in Lectures on Condensed Mathematics):

An analytic ring map $\mathcal{A}\to\mathcal{B}$ is called proper if the analytic structure of the latter ring is induced from the former, i.e. $\mathcal{B}=\mathcal{A}\otimes_\underline{\mathcal{A}}\underline{\mathcal{B}}$. (Maybe one should ask for steadiness in addition.) This is clearly stable under base change. An analytic space map $f\colon X\to Y$ is called partially proper if for affine open $V\subseteq Y$, $f^{-1}(V)$ can be covered by affine opens proper over $V$, and proper if it is quasicompact, quasiseperated, and partially proper. (Maybe one should ask for seperatedness.) For proper $f$, it is easy to see that $f_*\colon\mathsf{D}(X)\to\mathsf{D}(Y)$ commutes with $\mathsf{CondAni}$-tensoring on both sides, so we can reasonably call it $f_!$ and take right adjoint $f^!$. For partially proper $f$ and affine $Y$, one can define $f_!$ as the left Kan extension of $f_*$ from the stable subcategory generated by $j_*\mathsf{D}(U)$ where $j\colon U\hookrightarrow X$ runs over the open affines proper over $Y$. This coincides with the definition in Masterclass in Condensed Mathematics Session 19&20 in case of Riemann surface, if I did not go wrong.

Define the compactification $\overline{\mathcal{B}}^{/\mathcal{A}}=\mathcal{A}\otimes_\underline{\mathcal{A}}\underline{\mathcal{B}}$. If $\underline{\mathcal{B}}\in\mathsf{D}(\mathcal{A})$ is nuclear, then this is steady over $\mathcal{A}$; if moreover $\mathcal{B}$ is steady over $\mathcal{A}$, then the canonical map $\overline{\mathcal{B}}^{/\mathcal{A}}\to\mathcal{B}$ is a steady localization, and one can prove that in this case the compactification of a steady localization is again a steady localization, so it can be globalized.

This is motivated by the discussion of discrete adic space in Lectures on Condensed Mathematics, and it covers both discrete adic space and complex-analytic geometry; but when trying to copy $j_!$ from there, a problem arises: In general there might be nothing like $\mathcal{B}_{\infty/\mathcal{A}}$ for steady localizations, even in the case the underlying condensed rings are the same; so $j^*$ lacks a left adjoint.

So the questions are:

  1. How generally are this "properness" and the six-functor formalism reasonable, or we have to work case by case in several kinds of geometry? I think it should also work for rigid-analytic geometry.

  2. Perfectoid spaces and rigid-analytic spaces can be made analytic spaces. Does this "properness" coincide with that of diamonds?

  3. Is it reasonable to talk about étale sheaves on analytic spaces, or the analytic formalism is way too general?

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    $\begingroup$ Good question! In Etale cohomology of diamonds, a notion of "compactifiable" morphisms is constructed, asking that the map to this kind of "canonical compactification" is an open immersion. I think you can ask the same here, where "open immersion" should be understood as the existence of a left adjoint of $j^\ast$. It is probably true that these notions agree with the existing notions for adic spaces, and that this is good enough for an $f_!$ functor. But I would have to think more about this. $\endgroup$ Commented Aug 27, 2021 at 9:57
  • $\begingroup$ Sorry, what do you mean by "coinciding with ... Riemann surfaces"? For example, what are "affine opens" in complex analytic geometry? I would guess, by mimicking Clausen's lecture, that for complex manifolds, they might be closed polydiscs (so not open) with the ring of overconvergent power series. This seems to coincide with Lurie's result that Clausen mentioned in the lectures if we need to compare it with classical "opens". $\endgroup$
    – Z. M
    Commented Aug 27, 2021 at 16:49
  • $\begingroup$ @Z.M Here the map considered is from a Riemann surface to a point. "Affine opens proper over Y" is just analytic spectra of overconvergent rings. I am viewing analytic spaces as locally analytically ringed locales to talk about openness. Actually the way to make a Riemann surface an analytic space is exactly to glue from analytic spectra of overconvergent rings on closed discs, so these serve as "affine opens" in analog with scheme theory. $\endgroup$ Commented Aug 27, 2021 at 21:29
  • $\begingroup$ Sorry, I am still confused. Let me restrict to Riemann surfaces. How do you talk about openness so that closed discs are open? One of the confusions is that, for a compact Hausdorff space, there are two sites: the site of open subsets, and the site of compact subsets. The sheaf on the former is equivalent to an overconvergent sheaf on the later (Lurie HTT 7.3.4), while both have a corresponding locale if I understand correctly. $\endgroup$
    – Z. M
    Commented Aug 28, 2021 at 12:17
  • $\begingroup$ A weaker question is whether (the AnSpec of) a closed disc (with overconvergent power series ring) in a Riemann surface a steady subspace? If this is the case, then the locale obtained in Clausen-Scholze is probably not the classical one (of open subsets). $\endgroup$
    – Z. M
    Commented Aug 28, 2021 at 12:24

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