categories - Category Theory list
 help / color / mirror / Atom feed
* Has anyone seen this condition?
@ 2008-05-16 21:04 Michael Barr
  0 siblings, 0 replies; only message in thread
From: Michael Barr @ 2008-05-16 21:04 UTC (permalink / raw)
  To: Categories list

In our (John Kennison, Bob Raphael, and I) work, the following condition
has arisen.  Has anyone seen or named it?  Say that an object E of a
category is a ???? if it is a cogenerator and if whenever f: A ---> B is
not an epimorphism and g: B ---> C is a regular monomorphism, then there
are two maps h,k: C ---> E s.t. hg is unequal to kg, while hgf = kgf.

This is related to the questions Paul Taylor and I have raised recently.

Theorem.  If E satisfies ????, then whenever A has an extremal
monomorphism into a power of E, then A ---> TA ===> T^2A is an equalizer
where T is the triple from the adjoint pair Hom(-,E) and E^{(-)}.

What's interesting is that while it is obvious that any injective
cogenerator satisfies ????, it is also the case that any cogenerator that
contains an injective cogenerator also satisfies ????.  Thus, in
completely regular spaces, the interval is a cogenerator and both it and
the real line (and many, many other spaces) also satisfy ????.

Michael




^ permalink raw reply	[flat|nested] only message in thread

only message in thread, other threads:[~2008-05-16 21:04 UTC | newest]

Thread overview: (only message) (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2008-05-16 21:04 Has anyone seen this condition? Michael Barr

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).