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[Merged by Bors] - feat(finite_dimensional/subalgebra) : add subalgebra.is_simple_order_of_finrank #17237

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@xroblot xroblot commented Oct 29, 2022

This PR adds some lemma that will be used in the proof (#17285) that two complex embeddings of a field define the same place iff they are equal or complex conjugate, mainly:

  • subalgebra.is_simple_order_of_finrank shows that the only two subalgebras in an algebra of dimension 2 are exactly and

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@xroblot xroblot changed the title feat() : add complex.subfield_eq_of_closed feat(finite_dimensional/subalgebra) : add subalgebra.eq_bot_or_top_of_finrank Oct 29, 2022
@xroblot xroblot marked this pull request as ready for review October 29, 2022 14:48
@xroblot xroblot changed the title feat(finite_dimensional/subalgebra) : add subalgebra.eq_bot_or_top_of_finrank feat(finite_dimensional/subalgebra) : add subalgebra.is_simple_order_of_finrank Oct 30, 2022
@xroblot xroblot added the awaiting-CI The author would like to see what CI has to say before doing more work. label Oct 31, 2022
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src/linear_algebra/finite_dimensional.lean Outdated Show resolved Hide resolved
Co-authored-by: Junyan Xu <junyanxumath@gmail.com>
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maintainer merge

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🚀 Pull request has been placed on the maintainer queue by alreadydone.

xroblot and others added 2 commits November 1, 2022 07:56
Co-authored-by: Eric Wieser <wieser.eric@gmail.com>
@xroblot xroblot added the awaiting-CI The author would like to see what CI has to say before doing more work. label Nov 1, 2022
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Comments are not loading on my phone so maybe you already addressed this: is there no subring.top_equiv that you can reuse for subfields?

@Vierkantor Vierkantor closed this Nov 2, 2022
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Comments are not loading on my phone so maybe you already addressed this: is there no subring.top_equiv that you can reuse for subfields?

LGTM otherwise!

bors d+

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bors bot commented Nov 2, 2022

✌️ xroblot can now approve this pull request. To approve and merge a pull request, simply reply with bors r+. More detailed instructions are available here.

@github-actions github-actions bot added delegated The PR author may merge after reviewing final suggestions. and removed awaiting-review The author would like community review of the PR labels Nov 2, 2022
@Vierkantor Vierkantor reopened this Nov 2, 2022
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xroblot commented Nov 2, 2022

Comments are not loading on my phone so maybe you already addressed this: is there no subring.top_equiv that you can reuse for subfields?

I found versions of top_equiv for subgroup, submonoid, submodule, subalgebra (and some other variations) but nothing for subring. I guess I could add it and use it to construct the field version if you think it is needed.

Well, I just did that :)

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That generality is much better, thanks! Once the build passes, please reply with bors merge to merge this pull request.

@github-actions github-actions bot removed the awaiting-CI The author would like to see what CI has to say before doing more work. label Nov 2, 2022
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xroblot commented Nov 2, 2022

bors merge

bors bot pushed a commit that referenced this pull request Nov 2, 2022
…of_finrank (#17237)

This PR adds some lemma that will be used in the proof (#17285) that two complex embeddings of a field define the same place iff they are equal or complex conjugate, mainly:
- `subalgebra.is_simple_order_of_finrank` shows that the only two subalgebras in an algebra of dimension 2 are exactly `⊥` and  `⊤`
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bors bot commented Nov 2, 2022

Pull request successfully merged into master.

Build succeeded:

@bors bors bot changed the title feat(finite_dimensional/subalgebra) : add subalgebra.is_simple_order_of_finrank [Merged by Bors] - feat(finite_dimensional/subalgebra) : add subalgebra.is_simple_order_of_finrank Nov 2, 2022
@bors bors bot closed this Nov 2, 2022
@bors bors bot deleted the xfr-place_eq_aux branch November 2, 2022 20:02
@eric-wieser eric-wieser added the hacktoberfest-accepted Without this label hacktoberfest is scared off by bors label Nov 5, 2022
bors bot pushed a commit that referenced this pull request Nov 19, 2022
…ision_ring and more (#17401)

+ Replace K by ℕ in two proofs in *linear_algebra/basis*, which immediately allows generalization from `division_ring` to `field` in *submodule/basic*, *field_theory/tower*, *linear_algebra/dimension*, *projective_space/basic*, *linear_algebra/finite_dimensional*, and *affine_space/finite_dimensional*. (~~@riccardobrasca authored many of these;~~ @semorrison made some `division_ring` generalizations a while ago; @adamtopaz's TODO in *projective_space/basic* is now resolved. Let me know if you can think of more stuff to generalize.)

+ Add `subalgebra.is_simple_order_of_finrank_prime` in *field_theory/tower*. Inspired by [#17237](#17237 (comment)) (@xroblot).

+ Make `subalgebra.to_submodule` an `order_embedding` in *subalgebra/basic*, remove lemmas rendered redundant, and fix things in *intermediate_field*, *field_theory/normal*, and *adjoin/fg*.

+ Changes in *linear_algebra/finite_dimensional* and *linear_algebra/finrank*:

    + Add `finite_dimensional_of_dim_eq_nat`: used to golf `finite_dimensional_of_dim_eq_zero/one`.

    + Add `submodule.finrank_le_finrank_of_le` and `finrank_lt_finrank_of_lt` which only assumes the larger submodule is finite rather than the whole module. Rename the original `finrank_lt_finrank_of_lt` to `finrank_strict_mono`, matching the existing `finrank_mono`.

    + Remove `subalgebra.dim/finrank_eq_one_of_eq_bot` which has a substitutable equality among its assumptions (use `dim/finrank_bot` instead).
   
    + Add `subalgebra.dim/finrank/finite_dimensional_to_submodule` and an instance `finite_dimensional_subalgebra` similar to [finite_dimensional_submodule](https://leanprover-community.github.io/mathlib_docs/linear_algebra/finite_dimensional.html#finite_dimensional.finite_dimensional_submodule).

    + Generalize `section subalgebra_dim` from `[field E]` to `[ring E]`, adding `[nontrivial E]` hypothesis whenever necessary.

    + Generalize `subalgebra.eq_bot_of_dim_one` to `of_dim_le_one` and golf the proof (together with `eq_bot_of_finrank_one`).

    + Move `finite_dimensional.of_subalgebra_to_submodule` from *splitting_field* to *finite_dimensional*.

+ Add `exists_nat_eq_of_le_nat` in *cardinal/basic*.

+ Fix a slow proof in *polynomial/bernstein*.



Co-authored-by: Xavier-François Roblot <46200072+xroblot@users.noreply.github.com>
Co-authored-by: Junyan Xu <junyanxu.math@gmail.com>
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