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feat(analysis/specific_limits/complex) #18887

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Louddy
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@Louddy Louddy commented Apr 27, 2023

This PR introduces a single new lemma about the limit of 1 / n as n → ∞ in the complex numbers. It has been placed in a new file for two reasons: the obvious file to put it (analysis/specific_limits/basic) does not have the required imports, and it also makes porting easier since basic has already been ported to mathlib4.

Note that this is a prerequisite for an upcoming PR for the Hadamard three-line theorem.

Finally, thanks to Patrick Massot for supplying the actual proof on Zulip a while back!


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Specific limits complex numbers
Prerequisite for upcoming Hadamard Three Lines Theorem.
Separate from basic to avoid adding dependencies.
Proof of lemma by Patrick Massot
@Louddy Louddy added awaiting-review The author would like community review of the PR t-analysis Analysis (normed *, calculus) labels Apr 27, 2023
@eric-wieser
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I'm surprised we can't state this more generally; is it true for any ℝ-algebra?

Added a lemma for the limit of `1/n` into an `ℝ` algebra.
@github-actions github-actions bot added the modifies-synchronized-file This PR touches a files that has already been ported to mathlib4, and may need a synchronization PR. label Apr 28, 2023
@loefflerd
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Why do you remove the TODO comment on the following lemma? I don't think this lemma solves that problem -- the point of the comment is that it would be nice to cover topological rings which aren't algebras over the reals.

@Louddy
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Louddy commented Apr 28, 2023

My mistake!

@eric-wieser eric-wieser added the not-too-late This PR was ready at the point mathlib3 was frozen: we will try to merge it and port it to mathlib4 label Jul 15, 2023
@semorrison
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I've created a zulip thread about this PR.

@j-loreaux
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I left a comment in the Zulip thread with a mathport oneshot output of this (which compiles), and that can be PR'ed directly to mathlib4.

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5 participants