Subject: Re: 2 responses
Date: Thu, 14 Mar 2002 11:03:10 -0500 (Eastern Standard Time)
From: "Nicholas J. Kuhn" <njk4x@tetra.mail.virginia.edu>
To: Don Davis <dmd1@lehigh.edu>
CC: njk4x@virginia.edu

A little comment about categories where morphisms are diagrams
       G_1 --> H <-- G_2   ...

This `category' is NOT a category in general, because the morphisms
from G_1 to G_2 will not be a set (and one bumps up against Russell's
paradox).  This, of course, is a well known and fundamental problem to
all who work with localizations and model categories.
   The simplest fix is to restrict the construction to a small category
(i.e. a set's worth of objects).

   Nick Kuhn