ScalingStacks

Proof of Proposition 4.5 . [01AP]

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Proof of Proposition 4.5.

As above let (φj)j(\varphi_{j})_{j} be a decreasing net of ω\omega-psh model functions converging to φ\varphi. After adding a constant we may assume that φj≤0\varphi_{j}\leq 0 for all jj. For each integer m≥1m\geq 1, the net (max⁡{φj,−m})j(\max\{\varphi_{j},-m\})_{j} decreases to the bounded ω\omega-psh function max⁡{φ,−m}\max\{\varphi,-m\}. We can therefore choose jmj_{m} such that

(4.1) 0≤∫(max⁡{φjm,−m}−max⁡{φ,−m})​MA⁡(max⁡{φ,−m}2)≤(2​m)−2n+1.0\leq\int\left(\max\{\varphi_{j_{m}},-m\}-\max\{\varphi,-m\}\right)\MA\left(\frac{\max\{\varphi,-m\}}{2}\right)\leq(2m)^{-2^{n+1}}.

We may further assume jm+1≥jmj_{m+1}\geq j_{m} for all mm. Set φm:=φjm\varphi_{m}:=\varphi_{j_{m}}. We claim that the decreasing sequence (φm)m=1∞(\varphi_{m})_{m=1}^{\infty} converges to φ\varphi. By Theorem 2.10 it suffices to test this at any divisorial point x∈Xx\in X. We have 0≥φ⁡(x)>−∞0\geq\varphi(x)>-\infty and φm​(x)≥φ⁡(x)≥−m\varphi_{m}(x)\geq\varphi(x)\geq-m for m≥−φ⁡(x)≥0m\geq-\varphi(x)\geq 0. By (4.1), Lemma 4.7 and the definition of capacity we get

0≤(φm​(x)−φ⁡(x))​Capω​{x}≤1m0\leq(\varphi_{m}(x)-\varphi(x))\Capa_{\omega}\{x\}\leq\frac{1}{m}

for m≥|φ⁡(x)|m\geq|\varphi(x)|. Now Capω⁡{x}>0\Capa_{\omega}\{x\}>0 by Lemma 4.2, thus φm​(x)\varphi_{m}(x) converges to φ⁡(x)\varphi(x), which concludes the proof. ∎

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