ScalingStacks

Proof. [02VM]

Original official author HTML, exact retained edition. Historical TeX conversion verdicts remain unchanged. Cited-edition alignment and mathematical self-containment are not assessed.

Complete original source context · Original author HTML

Proof.

By Proposition 3.77(2) and Proposition 3.80, the statements (1) and (2) are equivalent.

Let ∥⋅∥\|\cdot\| be an approachable toric metric. By Corollary 5.17 the function |ψ∥⋅∥−Ψ||\psi_{\|\cdot\|}-\Psi| is bounded. By approachability there is a sequence ∥⋅∥l\|\cdot\|_{l} of smooth (resp. algebraic) semipositive metrics that converges to ∥⋅∥\|\cdot\|. Since ∥⋅∥\|\cdot\| is toric, ∥⋅∥𝕊=∥⋅∥\|\cdot\|_{\mathbb{S}}=\|\cdot\|. Hence, the sequence of toric metrics (∥⋅∥l)𝕊(\|\cdot\|_{l})_{\mathbb{S}} also converges to ∥⋅∥\|\cdot\|. We denote ψl=ψ(∥⋅∥l)𝕊\psi_{l}=\psi_{(\|\cdot\|_{l})_{\mathbb{S}}}. By Proposition 5.38 and Proposition 5.67 the functions ψl\psi_{l} are concave. Since the sequence (ψl)l(\psi_{l})_{l} converge uniformly to ψ∥⋅∥\psi_{\|\cdot\|}, the latter is concave.

Let now ψ\psi be a concave function on NℝN_{\mathbb{R}} such that |Ψ−ψ||\Psi-\psi| is bounded. Then ψ\psi determines a metric ∥⋅∥\|\cdot\| on the restriction of LanL^{{\text{\rm an}}} to X0anX_{0}^{{\text{\rm an}}}. Since stab⁡(ψ)=stab⁡(Ψ)=ΔΨ\operatorname{stab}(\psi)=\operatorname{stab}(\Psi)=\Delta_{\Psi}, by Proposition 3.81 there is a sequence of rational piecewise affine concave functions ψl\psi_{l} that converge uniformly to ψ\psi and with rec⁡(ψl)=Ψ\operatorname{rec}(\psi_{l})=\Psi. By Remark 5.46, the functions Ψ−ψl\Psi-\psi_{l} can be extended to continuous functions on NΣN_{\Sigma}. Therefore, Ψ−ψ\Psi-\psi can be extended to a continuous function on NΣN_{\Sigma}. Consequently the metric ∥⋅∥\|\cdot\| can be extended to XanX^{{\text{\rm an}}}. Let ∥⋅∥l\|\cdot\|_{l} be the metric associated to ψl\psi_{l}. Then the sequence of metrics ∥⋅∥l\|\cdot\|_{l} converges to ∥⋅∥\|\cdot\|. By Corollary 5.28, the metrics ∥⋅∥l\|\cdot\|_{l} are approachable. We deduce that ∥⋅∥\|\cdot\| is approachable. ∎

Original mathematics by the credited authors. Source-backed reader collection; mathematical self-containment is not assessed.