From: categories <cat-dist@mta.ca>
To: categories <categories@mta.ca>
Subject: Re: question on finiteness in toposes
Date: Sat, 11 Jan 1997 13:15:36 -0400 (AST) [thread overview]
Message-ID: <Pine.OSF.3.90.970111131529.5778F-100000@mailserv.mta.ca> (raw)
Date: Sat, 11 Jan 1997 09:05:39 -0500 (EST)
From: Peter Freyd <pjf@saul.cis.upenn.edu>
Let me expand. If one bores into just why Set^2_kf can't be
boolean and looks for a minimal example of its non-booleaness
one inevitably lands on the object 2 -> 1. At first blush
its lattice of subobjects does look boolean. Until one notices
that there's a monomorphism from 2 -> 2 to 2 -> 1 (where
2 -> 2 is the identity map).
Having noticed that, one has a quicker proof that it's not a
topos: not every mono-epi is an equalizer.
next reply other threads:[~1997-01-11 17:15 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
1997-01-11 17:15 categories [this message]
-- strict thread matches above, loose matches on Subject: below --
1997-01-16 1:25 categories
1997-01-15 14:33 categories
1997-01-15 0:14 categories
1997-01-13 14:26 categories
1997-01-12 20:42 categories
1997-01-11 17:14 categories
1997-01-10 16:32 categories
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=Pine.OSF.3.90.970111131529.5778F-100000@mailserv.mta.ca \
--to=cat-dist@mta.ca \
--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).