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[Merged by Bors] - chore: Generalise monotonicity of multiplication lemmas to semirings #9369

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@YaelDillies YaelDillies commented Dec 31, 2023

Many lemmas about BlahOrderedRing α did not mention negation. I could generalise almost all those lemmas to BlahOrderedSemiring α + ExistsAddOfLE α except for a series of five lemmas (left a TODO about them).

Now those lemmas apply to things like the naturals. This is not very useful on its own, because those lemmas are trivially true on canonically ordered semirings (they are about multiplication by negative elements, of which there are none, or nonnegativity of squares, but we already know everything is nonnegative), except that I will soon add more complicated inequalities that are based on those, and it would be a shame having to write two versions of each: one for ordered rings, one for canonically ordered semirings.

A similar refactor could be made for scalar multiplication, but this PR is big enough already.

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Many lemmas about `BlahOrderedRing α` did not mention negation. I could generalise almost all those lemmas to `BlahOrderedSemiring α + `ExistsAddOfLE α` except for a series of five lemmas (left a TODO about them).

Now those lemmas apply to things like the naturals. This is not very useful on its own, because those lemmas are trivially true on canonically ordered semirings (they about multiplication by negative elements, of which there are none, or nonnegativity of squares, but we already know everything is nonnegative), except that I will soon add more complicated inequalities that are based on those, and it would be a shame having to write two versions of each: one for ordered rings, one for canonically ordered semirings.

A similar refactor could be made for scalar multiplication, but this PR is big enough already.

From LeanAPAP
@YaelDillies YaelDillies added awaiting-review The author would like community review of the PR t-algebra Algebra (groups, rings, fields etc) t-order Order hierarchy labels Dec 31, 2023
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Thanks 🎉

bors merge

@leanprover-community-mathlib4-bot leanprover-community-mathlib4-bot added ready-to-merge This PR has been sent to bors. and removed awaiting-review The author would like community review of the PR labels Jan 1, 2024
mathlib-bors bot pushed a commit that referenced this pull request Jan 1, 2024
…9369)

Many lemmas about `BlahOrderedRing α` did not mention negation. I could generalise almost all those lemmas to `BlahOrderedSemiring α` + `ExistsAddOfLE α` except for a series of five lemmas (left a TODO about them).

Now those lemmas apply to things like the naturals. This is not very useful on its own, because those lemmas are trivially true on canonically ordered semirings (they are about multiplication by negative elements, of which there are none, or nonnegativity of squares, but we already know everything is nonnegative), except that I will soon add more complicated inequalities that are based on those, and it would be a shame having to write two versions of each: one for ordered rings, one for canonically ordered semirings.

A similar refactor could be made for scalar multiplication, but this PR is big enough already.

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mathlib-bors bot commented Jan 1, 2024

Pull request successfully merged into master.

Build succeeded!

And happy new year! 🎉

@mathlib-bors mathlib-bors bot changed the title chore: Generalise monotonicity of multiplication lemmas to semirings [Merged by Bors] - chore: Generalise monotonicity of multiplication lemmas to semirings Jan 1, 2024
@mathlib-bors mathlib-bors bot closed this Jan 1, 2024
@mathlib-bors mathlib-bors bot deleted the semiring_exists_add_of_le branch January 1, 2024 08:08
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