From: Jeff Egger <jeffegger@yahoo.ca>
To: categories list <categories@mta.ca>
Subject: Of chickens and eggs [was: is 0 prime?]
Date: Tue, 2 Oct 2007 18:29:58 -0400 (EDT) [thread overview]
Message-ID: <E1IcsDp-0001ON-FI@mailserv.mta.ca> (raw)
--- Vaughan Pratt <pratt@cs.stanford.edu> wrote:
> Presumably by Sup you mean what Peter Johnstone calls CSLat,
> complete semilattices, which is a lovely self-dual category.
Yes, indeed I did provide an equivalent definition:
> > [Sup denotes the category of complete lattices and sup-homomorphisms.]
> According it the status of "the most awesome" however is a symptom of
> not yet having come to grips with the joy of Chu,
At the risk of appearing pretentious, I'd like to quote Chekhov: de gustibus,
aut bene aut nihil. ;)
[Incidentally, I do like Chu categories, but I will play devil's advocate
here.]
> a more awesome
> self-dual category (fully) embedding CSLat in a duality-preserving and
> concrete-preserving way
...but not tensor-preserving? I could just as easily say that Chu(Set,2)
is (equivalent to) a lluf subcategory of Rel^2 (2 here denoting the arrow
category), which is in turn (equivalent to) a full subcategory of Sup^2;
the latter carries a fascinating *-autonomous structure derived from those
of Sup and 2, and the composite embedding is duality-preserving (though only
the first part is "concrete-preserving").
> [...] which is more awesome but still not awesome to the max.
Word.
> If going up only reduces the awe, then one should instead go down from
> CSLat for greater awe.
The trouble with (Dedekind-)infinite things is that one can argue about
which way is up and which way is down. For example, both the forgetful
functor Sup ---> Pos, and its left adjoint can be regarded as "embeddings"
---thus one could perversely regard complete (semi)lattices as more, not
less, general than arbitrary posets.
> Not only am I not a ring theorist but it's never occurred to me even to
> play one on the Internet.
I hope no-one would accuse me of "playing the ring theorist" on the
Internet or elsewhere, merely as a result of quoting some of the subject's
most celebrated theorems. [I was glad to learn that I have forgotten a
smaller chunk of my undergraduate education than I would have suspected.]
Cheers,
Jeff.
P.S. It has been pointed out to me, by a reader of this list, that the
"conventional wisdom" I quoted in re the history of ideal theory is
flawed (as I suspected, for no deeper reason than a profound mistrust
of conventional wisdom).
> > [...] is commonly cited as Dedekind's original motivation
> > for defining ideals.
>
> Hi Jeff,
> in fact Kummer defined ideal numbers and proved the Fermat
> conjecture for regular primes before Lame' presented the
> fallacious argument (by some years, I think, but I can't recall
> just how many). There's a lot of information about this in
> the Edwards book named after the conjecture (and some more in
> his recent book on constructive algebra).
next reply other threads:[~2007-10-02 22:29 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2007-10-02 22:29 Jeff Egger [this message]
2007-10-03 8:27 Vaughan Pratt
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