* Re: "compact", "rigid", or "autonomous"?
@ 2010-05-13 17:37 John Baez
2010-05-14 15:34 ` Chris Heunen
0 siblings, 1 reply; 2+ messages in thread
From: John Baez @ 2010-05-13 17:37 UTC (permalink / raw)
Mike wrote:
One reason I like "autonomous" to mean a symmetric monoidal category in
> which all objects have duals is that the only alternative names I have heard
> for such a thing convey misleading intuition to me. They are sometimes
> called "compact closed" or (I think) "rigid" monoidal categories...
Yes, I think "rigid" is traditional in algebraic geometry. Perhaps some
wiser head could explain how it originated!
Personally I often use "compact', since "compact closed" seems redudant.
And if I were king of the world, I'd use "with duals for objects".
Regarding the relation of this use of "compact" to the use in topology:
The only relationship I can think of is that a
>
compact subset of a Hausdorff space is closed, and a symmetric monoidal
> category with duals for objects is also automatically closed, but of course
> these two meanings of "closed" are totally different. Perhaps someone
> can enlighten me?
>
I don't know if this is what people were thinking when they first applied
"compact" to categories, or just my own rationalization, but:
A compact subset is closed, but it has a very nice property: its image under
any continuous map is again closed. Similarly a compact category is a
closed, but it has a very nice property: its essential image under any
symmetric monoidal functor is again compact.
I don't claim this justifies the terminology, but it helped me learn to live
with it.
Best,
jb
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* Re: "compact", "rigid", or "autonomous"?
2010-05-13 17:37 "compact", "rigid", or "autonomous"? John Baez
@ 2010-05-14 15:34 ` Chris Heunen
0 siblings, 0 replies; 2+ messages in thread
From: Chris Heunen @ 2010-05-14 15:34 UTC (permalink / raw)
To: categories
> I don't know if this is what people were thinking when they first
> applied "compact" to categories
As far as I'm aware, the terminology "compact" for categories came about
via representation theory: the finite-dimensional unitary
representations of a group form a category with certain properties, and
the group can be reconstructed from that category when the group is
compact. It seems the name transferred from groups to such categories.
But I wouldn't claim historical correctness; perhaps someone has the
definitive word about the origin of this terminology?
Best,
Chris
[For admin and other information see: http://www.mta.ca/~cat-dist/ ]
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