From: Michael Barr <mbarr@math.mcgill.ca>
To: Categories list <categories@mta.ca>
Subject: Re: Name of concept?
Date: Fri, 30 Sep 2005 14:37:14 -0400 (EDT) [thread overview]
Message-ID: <Pine.LNX.4.44.0509301426000.30909-100000@triples.math.mcgill.ca> (raw)
In-Reply-To: <Pine.LNX.4.44.0509291802530.22706-100000@triples.math.mcgill.ca>
Incidentally, did you know that if Z and Z' are defined so that
a d a'
0 --> Z ---> C ---> C ---> Z' ---> 0
is exact, then the homology is the image (= coimage) of a'.a: Z --> Z'?
This is a triviality, but it gives a symmetric definition of homology.
Notice that it defines something even when d.d is not 0. I guess it is Z
mod Z meet ker(d).
Mike
next prev parent reply other threads:[~2005-09-30 18:37 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2005-09-29 22:15 Michael Barr
2005-09-30 18:37 ` Michael Barr [this message]
2005-10-03 15:15 Marco Grandis
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