Derek Elkins <[EMAIL PROTECTED]> wrote: > Jason Dusek wrote: >> What about the part that reads: >> >> The unique arrow f making this diagram commute is then >> correspondingly denoted f1 ∐ f2 or f1 ⊕ f2 or f1 + f2 or >> [f1, f2] >> >> This would seem to say that [f,g] and f+g are the same thing >> -- but if I've understood Derek Elkins' remarks, the latter is >> the functorial action on arrows while the former is just the >> mediating arrow. > > In my experience the functorial action of a functor on arrows almost > always has the same symbol as the action on objects. Furthermore, I > don't think I've ever seen an example where the symbol used for the > action on objects was used for something other than the action on > arrows. I do think I have seen examples when a different symbol was > used. If A+B is used then f+g should be the action on arrows. > > Admittedly wikipedia does violate this. Perhaps it's using conventions > from some branch that I'm not familiar with. Maybe it is just silly.
Indeed. Using f1 ∐ f2 or f1 + f2 for the mediating arrow is confusing, to say the least. -- _jsn
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