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[Merged by Bors] - feat(archive/100-theorems-list/73_ascending_descending_sequences): Erdős–Szekeres #3074
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My worry, just glancing at this, is that the proof will be hard to maintain. It's a very long proof with few intermediate statements and no comments explaining the proof sketch. Do you think you could split this up a bit more? Or at the very least add comments inside the proof so readers have some landmarks? |
I don't think it'd be possible to split the proof up, but it should be very easy to add a sketch at the top and comments during the proof, I'll do that. |
The Wikipedia proof you refer to uses the pigeonhole principle. Do we have a reasonable API for making arguments with it in mathlib yet? cf. #2272. |
No, but this argument uses a very basic version which is basically just the cardinality of the image of an injective function |
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I think it should be straightforward to split up. Essentially every |
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Co-authored-by: Scott Morrison <scott.morrison@gmail.com>
I think still to do:
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The comments help a lot, thanks. My biggest worry is the long I didn't look at it in an editor and can't judge very well from the script (which is a minor warning sign itself), but maybe it would be possible to break the |
This block does close the two goals it's working on - should I add a comment to make that more clear? |
Sure, thanks. |
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Just some final cosmetic suggestions. Everything else looks good to me!
bors d+
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✌️ b-mehta can now approve this pull request. To approve and merge a pull request, simply reply with |
Co-authored-by: Bryan Gin-ge Chen <bryangingechen@gmail.com>
bors r+ |
…dős–Szekeres (#3074) Prove the Erdős-Szekeres theorem on ascending or descending sequences
Build failed: |
Co-authored-by: Bryan Gin-ge Chen <bryangingechen@gmail.com>
Oh, the latest commit on this branch might fail to build because we haven't merged master into this branch yet. I'm betting the merge commit will build though: |
…dős–Szekeres (#3074) Prove the Erdős-Szekeres theorem on ascending or descending sequences
Pull request successfully merged into master. Build succeeded: |
…dős–Szekeres (leanprover-community#3074) Prove the Erdős-Szekeres theorem on ascending or descending sequences
Prove the Erdős-Szekeres theorem on ascending or descending sequences
Can probably be golfed, but crossing another one off the Freek list