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proof of L'Hopital rule #1371

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ndslusarz
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Motivation for this change

Co-authored by: @affeldt-aist @hoheinzollern

Proofs of L'Hopital rule for limits taken on left and right, and Cauchy's mean value theorem.

Checklist
  • added corresponding entries in CHANGELOG_UNRELEASED.md
  • added corresponding documentation in the headers

Reference: How to document

Reminder to reviewers

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Main comment is about weakening nbhs a U to be only on the side of the limit. But generally happy to see more foundational calc stuff happening

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Section lhopital.
Context {R : realType}.
Variables (f df g dg : R -> R) (a : R) (U : set R) (Ua : nbhs a U).
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As usual, a question about boundary conditions. I'm a bit surprised to see we require f to be derivable in a full neighborhood of a. But then only take the right/left limit. Instead I would expect to see either a^'- U or a^'+U depending on the direction of the limit. Will the theorem still go through with that weakening?

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Good catch - I think this should go through, but changes are a bit more time-consuming than I expected so still in progress, should be done sometime next week.

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@ndslusarz do you have progress to share?

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Sorry, forgot to send an update before xmas - unfortunately not a major update, haven't been able to make it work for the restricted neighbourhoods (but still think it should be possible, so I'll get back on that). I could push the unfinished version in the meantime if you'd like?

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Yes.

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Pushed.

@affeldt-aist
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moved the lemmas to derive.v which is earlier in the file hierarchy, removed dead code in Cauchy's MVT, fix doc and changelog, but couldn't use left/right filters to generalize the proof yet

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3 participants