From: Vaughan Pratt <pratt@cs.stanford.edu>
To: Categories list <categories@mta.ca>
Subject: Re: A question on adjoints
Date: Wed, 19 Mar 2008 16:41:07 -0700 [thread overview]
Message-ID: <E1JcLUI-0004tm-7j@mailserv.mta.ca> (raw)
So it *is* a counterexample---to the notion that any old graph theorist
can do category theory. Focusing on the naturality, I forgot about
functoriality (done that before). More embarrassing is not thinking to
perform the easiest test of all category theory, F(0) = 0. And most
embarrassing is thinking that Mike could have overlooked such an easy
example. Sorry, Mike!
Vaughan
Michael Barr wrote:
> Actually, F isn't even a functor. The unique arrow 0 --> Ub has to give
> a canonical arrow F0 = 1 --> b, which there isn't.
next reply other threads:[~2008-03-19 23:41 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2008-03-19 23:41 Vaughan Pratt [this message]
-- strict thread matches above, loose matches on Subject: below --
2008-03-19 18:43 Michael Barr
2008-03-19 5:43 Vaughan Pratt
2008-03-18 18:11 Michael Barr
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