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[Merged by Bors] - chore(topology/algebra/infinite_sum): small todo #7994

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[Merged by Bors] - chore(topology/algebra/infinite_sum): small todo #7994

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@hrmacbeth hrmacbeth commented Jun 19, 2021 •
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Generalize a lemma from f : ℕ → ℝ to f : β → α, with

[add_comm_group α] [topological_space α] [topological_add_group α] [t2_space α] [decidable_eq β]

This was marked as TODO after #6017/#6096.

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@adomani, I assume this lemma is from the LTE. I hope the application there will work without change after this generalization, can you check?

@hrmacbeth hrmacbeth changed the title chore(topology/algebra/infinite_sum): small todo from #6017/#6096 chore(topology/algebra/infinite_sum): small todo Jun 19, 2021
@hrmacbeth hrmacbeth added the awaiting-review The author would like community review of the PR label Jun 19, 2021
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adomani commented Jun 19, 2021

Heather, actually, this lemma was useful for the proof of the existence of Liouville numbers, but I have not worked on finishing those PRs in a while: go ahead with the change and I will get back to Liouville once I get a chance!

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I am not sure that you prefer the exact terms, instead of the automated tactics, so feel free to disregard my suggestions!

Otherwise, this looks good to me!

(I am going to click on "Approve", just to see what it does, since I cannot really approve the changes anyway! (-: )

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eric-wieser
eric-wieser reviewed Jun 19, 2021
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src/topology/algebra/infinite_sum.lean Outdated
lemma has_sum_ite_eq_extract [decidable_eq β] (hf : has_sum f a) (b : β) :
has_sum (λ n, ite (n = b) 0 (f n)) (a - f b) :=
begin
convert has_sum_subtype_iff_indicator.mp (({b} : finset β).has_sum_iff_compl.mp hf),
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In the original #6017 PR I suggested a proof that notes that has_sum (function.update f b 0) is has_sum (λ n, ite (n = b) 0 (f n)), and uses has_sum.update. Does that proof work here?

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Probably (it'd be the same typeclass assumptions), but it doesn't seem like an obvious improvement?

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Co-authored-by: damiano <adomani@gmail.com>
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Thanks @adomani!

(I am going to click on "Approve", just to see what it does, since I cannot really approve the changes anyway! (-: )

I think clicking "Approve" is about the same as saying "LGTM", both are useful flags for the maintainers!

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bors bot commented Jun 20, 2021

✌️ hrmacbeth can now approve this pull request. To approve and merge a pull request, simply reply with bors r+. More detailed instructions are available here.

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bors d+

@github-actions github-actions bot added delegated The PR author may merge after reviewing final suggestions. and removed awaiting-review The author would like community review of the PR labels Jun 20, 2021
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Update src/topology/algebra/infinite_sum.lean
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Co-authored-by: Eric Wieser <wieser.eric@gmail.com>
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bors r+

@github-actions github-actions bot added the ready-to-merge All that is left is for bors to build and merge this PR. (Remember you need to say `bors r+`.) label Jun 20, 2021
bors bot pushed a commit that referenced this pull request Jun 20, 2021
@hrmacbeth
chore(topology/algebra/infinite_sum): small todo (#7994)
e1ca0ab 
Generalize a lemma from `f : ℕ → ℝ` to `f : β → α`, with 
```lean
[add_comm_group α] [topological_space α] [topological_add_group α] [t2_space α] [decidable_eq β] 
```
This was marked as TODO after #6017/#6096.
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bors bot commented Jun 20, 2021

Build failed (retrying...):

bors bot pushed a commit that referenced this pull request Jun 21, 2021
@hrmacbeth
chore(topology/algebra/infinite_sum): small todo (#7994)
4d69b0f 
Generalize a lemma from `f : ℕ → ℝ` to `f : β → α`, with 
```lean
[add_comm_group α] [topological_space α] [topological_add_group α] [t2_space α] [decidable_eq β] 
```
This was marked as TODO after #6017/#6096.
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bors bot commented Jun 21, 2021

Pull request successfully merged into master.

Build succeeded:

@bors bors bot changed the title chore(topology/algebra/infinite_sum): small todo [Merged by Bors] - chore(topology/algebra/infinite_sum): small todo Jun 21, 2021
@bors bors bot closed this Jun 21, 2021
@bors bors bot deleted the tsum_ite_eq_extract branch June 21, 2021 08:39
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