ScalingStacks

Proof of Theorem 5.11 . [01G2]

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Proof of Theorem 5.11.

. Suppose that φ∈𝒟⁡(X)\varphi\in\mathcal{D}(X) is a pointwise limit of θ\theta-psh model functions. Our goal is to show that φ\varphi is θ\theta-psh. Upon replacing θ\theta with θ+d​dc​φ\theta+dd^{c}\varphi we may assume that φ=0\varphi=0. Note that the existence of at least one θ\theta-psh model function implies that (θ𝒳)|𝒳K(\theta_{\mathcal{X}})|_{\mathcal{X}_{K}} is nef. As in Proposition 5.8 we can choose finitely many ample line bundles 𝒜i∈Pic⁡(𝒳)\mathcal{A}_{i}\in\Pic(\mathcal{X}) such that their numerical classes αi∈N1​(𝒳/S)\alpha_{i}\in N^{1}(\mathcal{X}/S) form a basis of N1​(𝒳/S)N^{1}(\mathcal{X}/S). There exists arbitrarily small positive numbers ε=(εi)\varepsilon=(\varepsilon_{i}) such that θ𝒳+∑iεi​αi\theta_{\mathcal{X}}+\sum_{i}\varepsilon_{i}\alpha_{i} is a rational class, hence the class of a 𝐐\mathbf{Q}-line bundle ℒε\mathcal{L}_{\varepsilon} on 𝒳\mathcal{X} whose restriction to 𝒳K\mathcal{X}_{K} is ample. Since 00 is a pointwise limit of θ\theta-psh model functions and since hℒε​e−ψh_{\mathcal{L}_{\varepsilon}}e^{-\psi} is semipositive for each θ\theta-psh model function ψ\psi, we may now apply Lemma 5.12 to conclude that ℒε\mathcal{L}_{\varepsilon} is nef. It follows that θ𝒳∈Nef⁡(𝒳/S)\theta_{\mathcal{X}}\in\Nef(\mathcal{X}/S) by closedness of the nef cone. ∎

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