From: categories <cat-dist@mta.ca>
To: categories <categories@mta.ca>
Subject: Re: Morphisms of diagrams
Date: Fri, 21 Mar 1997 14:00:01 -0400 (AST) [thread overview]
Message-ID: <Pine.OSF.3.90.970321135952.19578C-100000@mailserv.mta.ca> (raw)
Date: Fri, 21 Mar 97 15:15:56 +1100
From: Max Kelly <kelly_m@maths.su.oz.au>
Charles Wells asked the following:
__________
Let C be a category and I and I' graphs (or categories if
you prefer). Define a morphism of diagrams
psi:(delta:I-->C)-->(delta':I'-->C) to be a graph morphism (or
functor if you prefer) psi:I-->I' together with a natural
transformation alpha:delta' o psi-->delta. This definition
turns Lim into a contravariant functor from the category of
diagrams to C (when C is complete, anyway).
I believe this construction has been familiar since the early
days of category theory, but I don't know a reference and would
be glad to learn of any.
______________
Steve Lack replied with the folowing information:
____________
The dual construction (i.e. for colimits) appears in
Rene Guitart, ``Remarques sur les machines et les
structures'', Cahiers XV-2 (1974);
and its sequel
Rene Guitart and Luc Van den Bril, ``Decompositions
et lax-completions'', Cahiers XVIII-4 (1977);
where further references are also given.
_____________
I am writing at the university, with my files at home; but my
memory is that the construction was introduced by Eilenberg
and Mac Lane in 1945, in a paper called something like "On a
general theory of natural equivalences".
Max Kelly.
next reply other threads:[~1997-03-21 18:00 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
1997-03-21 18:00 categories [this message]
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1997-03-20 17:31 categories
1997-03-18 15:24 categories
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