ScalingStacks

Proof. [02CV]

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Proof.

Since the problem is local, we may assume for all r≤1r\leq 1 that the above map ϕr\phi_{r} exists and ϵ⁡(1)\epsilon(1) is as small as we like. For simplicity we denote ϕk=ϕ10−k\phi_{k}=\phi_{10^{-k}}, and ϵk=ϵ⁡(10−k)\epsilon_{k}=\epsilon(10^{-k}). Now we first define F0​(x)=ϕ0​(x)F_{0}(x)=\phi_{0}(x) on A^​(1,100)\hat{A}(1,100). Inductively suppose FkF_{k} is defined on A^​(10−k,10−k+2)\hat{A}(10^{-k},10^{-k+2}) satisfying Fk​(x)=ϕk∘Rk−1​(10k​x)F_{k}(x)=\phi_{k}\circ R_{k}^{-1}(10^{k}x) on A^​(10−k,20⋅10−k)\hat{A}(10^{-k},20\cdot 10^{-k}) for some rotation Rk∈O⁡(4)R_{k}\in O(4), then we apply Lemma 5.9 to the two maps ϕk∘Rk−1\phi_{k}\circ R_{k}^{-1} and ϕk+1\phi_{k+1} with r=10−kr=10^{-k} and ϵ=max⁡(ϵk−1,ϵk)\epsilon=\max(\epsilon_{k-1},\epsilon_{k}), and obtain a map fk+1f_{k+1} defined on A^​(1/10,100)\hat{A}(1/10,100) satisfying (2). Then we define Fk+1​(x)F_{k+1}(x) to be fk+1​(10k​x)f_{k+1}(10^{k}x) on A^​(10−k−1,10−k+1)\hat{A}(10^{-k-1},10^{-k+1}). By Lemma 5.9 we see that all the FkF_{k}’s match together to a map FF from B^∗\hat{B}^{*} to B⁡(q,200)B(q,200), and we can modify FF slightly near ∂B^\partial\hat{B} so that the image is exactly B∗B^{*}. It is easy to see that |F∗​g−g0|L∞​(A^​(10−k,10−k+1))=|102​k​fk+1∗​g−g0|L∞​(A^​(10,100))≤G⁡(max⁡(ϵk−1,ϵk))|F^{*}g-g_{0}|_{L^{\infty}(\hat{A}(10^{-k},10^{-k+1}))}=|10^{2k}f_{k+1}^{*}g-g_{0}|_{L^{\infty}(\hat{A}(10,100))}\leq G(\max(\epsilon_{k-1},\epsilon_{k})), and F∗​gF^{*}g extends to a continuous metric tensor over BB. ∎

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