I think, we should use ~=c instead of ~=g. So we have the ismorphisms
for any category.

Am 02.12.2024 um 18:23 schrieb Peter Dolland:

Steven, what do you think about

genCount = ( s e. _V |-> ( n e. NN |-> ( #  ( { e e. s | ( od  e ) = n
} /. ~=g ) ) ) )

? So, we would have

a1 = ( genCount ` Grp )
a688 = ( genCount ` Abel )
a122 = ( genCount ` Poset )

etc.

Am 27.11.2024 um 10:31 schrieb 'Peter Dolland' via Metamath:

Thank you, Steven, for formalizing oeis-a1! I think, there will be a
general counting function assigning to any extensible structure class
𝒞 and a given cardinality ק the cardinality of the quotient of the
subclass of 𝒞 having carrier sets with cardinality ק . The
restriction of this function to finite cardinalities will give the
OEIS sequences.

But first I have a few questions about using Metamath and set.mm:

(1) Is set.mm (without proofs) available as pdf? The book describes
how I can create LaTeX input for individual statements or proofs, but
not how the entire structure, including the important introductory
paragraphs, can be integrated. Cross references to definitions would
be nice.

(2) Either is there another tool to get the definition of a symbol in
a quick way? (also vim macros are welcome!)

(3) I would like to test your definition of a1. But I do not
understand, how to do this without changing set.mm. There is no
second read possible.

These are not the only questions I have when dealing with Metamath.
But I hope that answering them will make it a little easier for me to
get started.

Am 23.11.2024 um 19:51 schrieb Steven Nguyen:
As a current description, by default people work on their own
often-overlapping
topics, with the help of the community answering any questions. I'm
unsure so
I'll leave the question of contributors open.

The project proposed here seems highly interesting. I think the main
part
of the work is simply defining all the functions, since many
concepts haven't
been defined yet.

One potential difficulty is that Metamath currently does not have
much tooling.
So computer-generated proofs are ironically tedious and manual to
prove by
default (not sure if https://us.metamath.org/mpeuni/631prm.html was done
manually; https://us.metamath.org/mpeuni/ax-bgbltosilva.html is also
illustrative).
Computer-generated proofs are rare in math, luckily. But if the plan
is to prove a
very large amount of sequences then I imagine it would be more
efficient to make
the tooling for it first. Or (dun dun dun?) ask the Lean community.
Teamwork
makes the dream work, in this case the sequences are
math-community-wide so
I'd imagine the larger amount of people doing Lean proofs would make
it easier.

I don't see any other strategy than starting with some sequence, and
start seeing
what needs to be done (a lot). As a start, here's A1, informally the
(number of groups of order N), the definition is
(number of groups of order N, mod equivalence)
a1 = ( n e. NN |-> ( # ` ( { g e. Grp | ( od ` g ) = n } /. ~=g ) ) )
On Thursday, November 21, 2024 at 10:54:30 AM UTC-6 Peter Dolland wrote:

    Hello Metamath Community,

    I'm still new here. So let me explain my intention, what I want
    here. My
    original motivation comes from combinatorics. I am interested in
    the
    relationship between the specification of an algebraic structure
    (such
    as directed or undirected graph, magma resp. groupoid,
    semigroup, group,
    topological space, partition, etc.) and the sequence that
    indicates how
    many non-isomorphic instances of the structure there are over a
    set with
    n elements, where n=0,1,2,3,.... . These sequences are published on
    oeis.org <http://oeis.org>: A273, A88, A1329, A27851, A1, A1930,
    A41,... . For some of
    them, a generating algorithm (in some programming language) is also
    given. However, in none of these sequences is a formal
    specification of
    the underlying algebraic structure given, although this is often
    much
    simpler than the generating algorithm.

    My impression so far is that the desired specifications can be
    created
    with MetaMath without any effort, as long as they are not already
    contained in set.mm <http://set.mm>. A real challenge would
    probably be to verify the
    specified algorithms against the specifications. It seems to me
    that a
    basis of theorems would have to be created first. In particular,
    Polya's
    counting theorem would need to be formalised. But perhaps one of
    you
    knows what already exists on this topic and can be used.

    Irrespective of this, it also seems worthwhile to me to create a
    bridge
    between MetaMath and OEIS in such a way that MetaMath
    specifications are
    added to corresponding sequences. The aim here could be to
    improve the
    findability of sequences. For example, the additional criterion
    that the
    elements of the carrier set are to be regarded as different
    (labelled)
    could be achieved by adding an independent complete order
    relation. For
    example, compare the sequences A88 with A53763, A273 with A2416,
    A41
    with A110 or A1930 with A798. So you can see the first sequence
    is for
    each pair the unlabelled version. And the second ones yield the
    labelled
    version.

    I see a need for action that goes far beyond my areas of different
    expertises. The question now arises as to whether there are
    people in
    your community who are willing and able to support me in my
    search of a
    bridge as mentioned above. I have to admit that I have not yet
    delved
    very deeply into MetaMath and set.mm <http://set.mm>. If I find
    someone here, I really
    will have chance in order to acquire the necessary knowledge and
    skills.
    I am hopefully very convinced that MetaMath makes a decisive
    contribution to the further development of mathematics and computer
    science by formalising important statements.

    With best wishes,
    Peter Dolland

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