Hi metakunt,

Sorry I don't have much time this week for a long answer.

I think the best course of action would be to identify a good reference
textbook, and follow along with the definitions and properties. I cannot
help much with that choice as I'm not an expert in the domain.

Milne's course notes are available online, so using them will help
anyone who does not have access to a physical math library.

https://www.jmilne.org/math/CourseNotes/FT.pdf

Then other options that come to mind is simply to look at the references
listed in the Wikipedia page for Finite Fields... and ask the community,
like in this question:

https://mathoverflow.net/questions/126364/books-on-advanced-galois-theory

It's usually easier to go from the more general to the "numerical"
application, so a general advice would be to not restrict yourself too
much to a single application.

Pulling `polyFld` into main or your own mathbox and starting proving
theorems like "a splitting field is a field", "a splitting field is a
field extension", etc. sounds like a great start.

BR,
_
Thierry



On 23/08/2024 18:30, 'Meta Kunt' via Metamath wrote:
­Hey guys,

I'd like to develop a nice API of Galois theory and algebraic
closures, in particular I want existence of primitive roots and some
group theory to count the number of elements satisfying a condition.

Most of the definitions are in Mario's mathbox. However since I don't
quite fully understand the intricacies of splitting field and direct
limits, I'd need some handholding.#
These definitions would need to be moved out of Mario's mathbox.
HomLimB,HomLim,polyFld,splitFld1,splitFld1,polySplitLim,gf,gfoo­

Also I'd like to know what the API of the theorems is that I need to
prove. I am certain that Mario's work is excellent, however based on
any definition I would struggle to develop any api.
If we could discuss what theorems we need to formalise to develop a
good API of the theory. But not only that, there will be lots of
connective work linking definitions to powerful theorems that use it.

As a goal I'd like to construct the field GF(4) and explicitly
calculate the elements of it. By Mario's definition this is the
splitting field of (X^4-X)=(X^2+X+1)(X-1)(X) so there is already a big
hurdle to overcome.
We could link the definition of GF(4) which would just be ( 2 GF 2 )
in set.mm
splitFld itself is another binary operation, this time substituted and
in prosa would be similar to metamaths ( Z_2 splitFld (X^4-X) )
We now inside splitFld get an isomorphism predicate that says that we
adjoin the roots in order, atleast that's what I think it does as (# `
p ) = 1 in our case. But the value is another more complicated map in what
appears to be adjoining either another more technical root or the
identity function and sequentially repeating the process.
It appears even crazier that splitFld1 chooses a monic irreducible
polynomial in a "canonical" way and then does a field extension with
that polynomial. After that I didn't bother to much understand it since
this is several layers too deep already.


The first goal, as funnily as it is, is to likely develop the api
bottom up, which means defining important lemmas for polyFld first.

I assume we shall be able to prove something like that.
Let K be a field let f in K[X] be monic and irreducible (note
irreducible is likely enough). Then K[X]/(f) is a field.

I'd then like to be able to prove following results:
( Z_2 polyFld (X^2+X+1) ) is a field, contains 4 elements and give a
description of how those 4 elements look.

Thank you.
metakunt


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