Talk:Compact closed category

trace
The definition here is not the usual definition of trace. Trace of f:A --> A should be a morphism I to I, where I is the unit for the monoidal structure. Think in Vect, where Vect(k,k) \cong k. Then tr(f) = e_A c (f # 1) n_A, where n and e are the coevaluation and evaluation maps, c is the braiding or symmetry, and "#" is the tensor product. This gives the usual notion of trace.

For traces in categories that are not compact, you need a pivotal structure.

Also, adjoint are of course only defined for morphisms. In order to say that an object is a left adjoint, you need to mention that you are looking at a monoidal category as a one-object bicategory. There is obviously no need for that, because you can define a left dual as you do.

Should say, adjoints are defined for functors, so if you want to say A^* is the left adjoint for A then it is better to say A^* \otimes - is the left adjoint of A \otimes -. Or indeed, explain the one object bicategory version. —Preceding unsigned comment added by 60.241.132.115 (talk) 11:12, 6 December 2007 (UTC)

Compact closed vs. Rigid
As someone pointed out on the rigid category page, these two articles may be referring to the same thing. It seems to me that they are, and they should be merged.

I see two small differences:
 * the condition that the monoidal category be symmetric in the compact closed article.
 * the definition of a dual is different: for the rigid article, a dual is merely the internal hom [X, 1], whereas in the compact closed article, a dual also includes the morphisms to the tensor product.

A closer look at references should help. Perhaps there are two conventions current for the definition of a dual, in which case they both need to be acknowledged.

Unique to the rigid article:
 * an alternative definition of a dual
 * Citation of the source of the definition of rigidity
 * Note that internal hom's exist in a rigid category

Unique to the compact category article:
 * Citation of original(?) source of definition of compact closed
 * Motivation for definition
 * Examples

There are also a few unique comments in both. The rest needs to be merged. Expz (talk) 13:35, 15 December 2009 (UTC)


 * The rigid article now has a section stating this: I quote:
 * Alternative Terminology A monoidal category where every object has a left (resp. right) dual is also sometimes called a left (resp. right) autonomous category. A monoidal category where every object has both a left and a right dual is sometimes called an autonomous category. An autonomous category that is also symmetric is called a compact closed category.
 * So, no merge. linas (talk) 02:15, 25 August 2012 (UTC)