Add Lean v3.20.0

[DonaldKellett]

Please complete the following information:

• Name: Lean
• Version: 3.20.0
• Release Note/Changelog: https://github.com/leanprover-community/lean/blob/master/doc/changes.md#3200c-9-september-2020

---

👍 reaction might help.

[DonaldKellett]

Please be informed that the Lean examples have been updated to use Lean v3.20.0 and the latest mathlib at the time of writing.

[kazk]

@DonaldKellett
mathlib example I've been using to test is failing with

unknown identifier 'one_div_pos_of_pos'
unknown identifier 'one_div_le_of_one_div_le_of_pos'

Something similar happened when adding v3.18.4 (codewars/codewars-runner-cli#828 (comment)).

Can you add simple mathlib example to your example repo? I just need something that uses mathlib to ensure it's correctly installed.
Adding a new Lean version will be smoother if you could maintain examples (including one using mathlib) and open issues after updating examples for the new version.

[DonaldKellett]

@kazk A minimal example involving mathlib has been added to the repo.

[kazk]

Thanks, I'll let you know when it's deployed.

[kazk]

Deployed. We have 21 kata to update https://github.com/codewars/codewars.com/wiki/List-of-Lean-Kata-to-Update