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From: Staffan Angere <staffan.angere@fil.lu.se>
To: "categories@mta.ca" <categories@mta.ca>
Subject: Isbell & MacLane on the insufficiency on skeletal categories
Date: Fri, 24 May 2013 22:34:47 +0000	[thread overview]
Message-ID: <E1UgG77-0001oH-8z@mlist.mta.ca> (raw)

Dear Category theorists,

in Categories for the Working Mathematician, page 164, MacLane relates an argument, "due to Isbell", why one cannot identify all isomorphic objects. I  have not, however, been able to find any publication of Isbell that contains the argument. Does anyone here know if he published it?

I also have a question about the argument itself: why is it made the way MacLane does it, rather than just though noticing that all functions from countable sets are countable, and thus themselves countable, and so isomorphic  to any other countable set? It seems like it would follow directly from this that any functions on the natural numbers have to be equal, if isomorphic (i.e. equinumerious) sets are identical. Why is MacLane doing all the "detours" though products, epics, etc.?

Thanks in advance,
Staffan

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             reply	other threads:[~2013-05-24 22:34 UTC|newest]

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2013-05-24 22:34 Staffan Angere [this message]
2013-05-25 15:47 ` Colin McLarty
2013-05-26 20:26   ` Bas Spitters
2013-06-06 22:00   ` Vaughan Pratt
2013-06-07  5:00     ` Colin McLarty
2013-06-07  3:15 Fred E.J. Linton

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