20 Jan
2007
20 Jan
'07
5:44 a.m.
"he knew it long before Grothendieck..."
So maybe the construction itself is obvious, particularly if you know the semi-direct product or some other specialization (of the general construction). But the intrinic characterization of what the construction yields, that is, the definition of a fibration, seems less obvious. I'm sure everyone has a favorite example of that. For example, Carsten Fuhrmann gave an intrinsic description of the Kleisli category of a monad only in 1999. His home page is: http://www.cs.bath.ac.uk/~cf/ David