Hi David, At 11:50 PM 12/3/2010, you wrote:
to push the chemical reaction analogy further, tensoring with an identity morphism 1_Y is like having a chemical present that doesn't take part in the reaction: it's there are the beginning and end, but doesn't change. But you can't take it away (and no, it's not like a catalyst, in that your original arrow f was there to begin with).
I agree completely. All I am saying is that since there is no effect on the reaction by the presence of a neutral chemical, it might just as well not be mentioned. Perhaps what I am getting at is a quotient category in which X@Y->Z@Y is identified with X->Z in this specific situation. I do believe this is how chemists think of their applications of Hess' Law, which is what my inquiry is really all about. Ellis [For admin and other information see: http://www.mta.ca/~cat-dist/ ]