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Anne's blog post on dedekind domains and class number #9

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Nov 22, 2021

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Vierkantor
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As requested, I wrote a bit on number theory, more specifically the Dedekind domain and class number formalization. The text is basically a summary of the class number paper, giving some mathematical background and pointing to the formal equivalents. I'm happy to have this blog post be edited mercilessly.

Is there a way to add commands like \Z = \mathbb{Z} in the math blocks?

Closes: #5

Alternatively, we can parse ((algebraic number) theory) as the area of mathematics studying [algebraic](https://leanprover-community.github.io/mathlib_docs/ring_theory/algebraic.html#is_algebraic) numbers, those satisfying a polynomial equation $f(\alpha) = 0$ for some nonzero polynomial $f$ with rational coefficients.
Algebraic numbers are found in [*number fields*](https://leanprover-community.github.io/mathlib_docs/number_theory/number_field.html#number_field), which are finite extensions of the field of rational numbers,
or equivalently fields generated by adjoining an algebraic element $\alpha$ to $\Q$ (by virtue of the [primitive element theorem](https://leanprover-community.github.io/mathlib_docs/field_theory/primitive_element.html#field.exists_primitive_element)).
Much like $\Q$ contains the integers $\Z$ as a subring, a number field $K$ contains a [*ring of integers*](https://leanprover-community.github.io/mathlib_docs/number_theory/number_field.html#number_field.ring_of_integers) $O_K$,
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I wonder if we want to use the find style links like docs# on zulip uses, to prevent these links breaking when they inevitably get moved between files.

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I agree with Eric's point, however I do think it's really cool that, like Wikipedia or nlab, we can talk about concepts and then directly link to them, so I absolutely think we should have some sort of link here.

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On the other hand, find might not help too much if we rename the defs as well. Perhaps the best solution is some form of link-integrity linter?

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Ideally we would have monthly archives for the documentation, so that we could link to the version of number_field from October 2021 and it will still work in October 2027 when we're done with the mathlib5 port.

Co-authored-by: Eric Wieser <wieser.eric@gmail.com>
Co-authored-by: Johan Commelin <johan@commelin.net>
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Very nice! I have made some comments about background and the way I look at things, see what you think.

posts/dedekind-domains-and-class-number-in-lean.md Outdated Show resolved Hide resolved
posts/dedekind-domains-and-class-number-in-lean.md Outdated Show resolved Hide resolved
Alternatively, we can parse ((algebraic number) theory) as the area of mathematics studying [algebraic](https://leanprover-community.github.io/mathlib_docs/ring_theory/algebraic.html#is_algebraic) numbers, those satisfying a polynomial equation $f(\alpha) = 0$ for some nonzero polynomial $f$ with rational coefficients.
Algebraic numbers are found in [*number fields*](https://leanprover-community.github.io/mathlib_docs/number_theory/number_field.html#number_field), which are finite extensions of the field of rational numbers,
or equivalently fields generated by adjoining an algebraic element $\alpha$ to $\Q$ (by virtue of the [primitive element theorem](https://leanprover-community.github.io/mathlib_docs/field_theory/primitive_element.html#field.exists_primitive_element)).
Much like $\Q$ contains the integers $\Z$ as a subring, a number field $K$ contains a [*ring of integers*](https://leanprover-community.github.io/mathlib_docs/number_theory/number_field.html#number_field.ring_of_integers) $O_K$,
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I agree with Eric's point, however I do think it's really cool that, like Wikipedia or nlab, we can talk about concepts and then directly link to them, so I absolutely think we should have some sort of link here.

posts/dedekind-domains-and-class-number-in-lean.md Outdated Show resolved Hide resolved
posts/dedekind-domains-and-class-number-in-lean.md Outdated Show resolved Hide resolved
Vierkantor and others added 4 commits October 8, 2021 11:24
Co-authored-by: Kevin Buzzard <k.buzzard@imperial.ac.uk>
Co-authored-by: Kevin Buzzard <k.buzzard@imperial.ac.uk>
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I went through and updated the blog post. The main change is a new paragraph on the timeout issues I ended up solving by defining ratfunc.

@PatrickMassot PatrickMassot merged commit afae7cb into master Nov 22, 2021
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Thanks a lot Anne!

@YaelDillies YaelDillies deleted the class-number branch June 12, 2024 07:51
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Anne on number theory
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