Mathlib v3 is deprecated. Go to Mathlib v4

Commit 2022-09-28 21:58 f7698588

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feat(tactic/push_neg): option for an alternate normal form of ¬ (P ∧ Q) (#16586) Backport a feature of the mathlib4 version of push_neg: an option to make ¬ (P ∧ Q) be normalized to ¬ P ∨ ¬ Q, rather than P → ¬ Q. That was actually the original behaviour, but it was changed in #3362. I have implemented this as a global option trace.push_neg.use_distrib (using the tracing option hack) rather than as a piece of configuration information which is passed when using the tactic, because I imagine this feature will mostly be used in teaching (that was both my motivation and also @PatrickMassot's when he wrote the original version), where it is convenient to "set it and forget it". This is also how it is implemented in the mathlib4 version (cc @dupuisf @j-loreaux). Zulip: https://leanprover.zulipchat.com/#narrow/stream/239415-metaprogramming-.2F-tactics/topic/alternative.20normal.20form.20for.20push_neg

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