From: Francois Lamarche <Francois.Lamarche@loria.fr>
To: categories@mta.ca
Subject: Monoidal structure, take II
Date: Thu, 18 Mar 1999 12:43:41 +0100 [thread overview]
Message-ID: <36F0E6ED.7EF7BB45@loria.fr> (raw)
Given the private replies I got to yesterday's queries, it is obvious I
was not clear enough, and indeed there was an unhelpful typo.
>
> I'm wondering, if anybody has ever described the following monoidal
> structure on the category of oriented multigraphs, what MacLane calls
> graphs, the most common kind of graph in category theory (but not
OK Saunders, from now on they're graphs. This what happens when you hang
out with combinatorists AND category theorists.
>
> Given graphs X, Y, the set |X-oY| of vertices on X-oY is the set of graph
> morphisms
> X --> Y.
So right from the start this is not the usual presheaf CC structure,
where the set of vertices is the set of all functions |X| --> |Y| .
So in what follows I use categorical notation for vertices, arrows, etc.
> Given f,g : X --> Y the set of arrows f-->g is the set of pairs
> (p_0,p_1) of functions such that
>
> forall x in |X|, p_0(x) : f(x)-->g(x)
>
> forall k: x-->y in X, p_1(k) : f(x)-->g(y)
Now the typo has been corrected. So an arrow f --> g is like a natural
transformation, with p_0 the usual familly of arrows indexed by the
vertices/objects of X, but since things don't compose, you add the
diagonal p_1 as part of the information. There is some kinship to
homotopies, as M. Barr has remarked.
> This co-contra bifunctor has a tensor left adjoint, which is symmetric
> and monoidal.
>
Is this more understandable?
Thanks again
Francois
next reply other threads:[~1999-03-18 11:43 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
1999-03-18 11:43 Francois Lamarche [this message]
1999-03-18 17:46 ` Michael Barr
1999-03-18 18:40 ` and there is a topological connection too Francois Lamarche
1999-03-18 17:27 Monoidal structure, take II Marco Grandis
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=36F0E6ED.7EF7BB45@loria.fr \
--to=francois.lamarche@loria.fr \
--cc=categories@mta.ca \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).