ScalingStacks

Theorem 2.7 . [02IP]

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Theorem 2.7.

Let XX be a scheme of finite type over KK and XanX^{{\text{\rm an}}} the associated analytic space.

  1. (1)

    XanX^{{\text{\rm an}}} is a locally compact and locally arc-connected topological space.

  2. (2)

    XanX^{{\text{\rm an}}} is Hausdorff (respectively compact and Hausdorff, arc-connected) if and only if XX is separated (respectively proper, connected).

  3. (3)

    The map π:Xan→X\pi\colon X^{{\text{\rm an}}}\to X is continuous. A locally constructible subset T⊂XT\subset X is open (respectively closed, dense) if and only if π−1​(T)\pi^{-1}(T) is open (respectively closed, dense).

  4. (4)

    Let ψ:X⟶Y\psi\colon X\longrightarrow Y be a morphism of schemes of finite type over KK and ψan:Xan⟶Yan\psi^{{\text{\rm an}}}\colon X^{{\text{\rm an}}}\longrightarrow Y^{{\text{\rm an}}} its analytification. Then ψ\psi is flat (respectively unramified, étale, smooth, separated, injective, surjective, open immersion, isomorphism) if and only if ψan\psi^{{\text{\rm an}}} has the same property.

  5. (5)

    Let K′K^{\prime} be a complete extension of KK. Then the map πK′:XK′an→XK′\pi_{K^{\prime}}:X^{{\text{\rm an}}}_{K^{\prime}}\to X_{K^{\prime}} induces a bijection between Xan​(K′)X^{{\text{\rm an}}}(K^{\prime}) and X⁡(K′)X(K^{\prime}).

  6. (6)

    Set Xalg={p∈X|[K(p):K]<∞}X_{{\text{\rm alg}}}=\{p\in X|\,[K(p):K]<\infty\}. Then π\pi induces a bijection between XalganX^{{\text{\rm an}}}_{{\text{\rm alg}}} and XalgX_{{\text{\rm alg}}}. The subset Xalgan⊂XanX^{{\text{\rm an}}}_{{\text{\rm alg}}}\subset X^{{\text{\rm an}}} is dense.

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