Re: A question on adjoints

So it *is* a counterexample---to the notion that any old graph theorist can do category theory. Focusing on the naturality, I forgot about functoriality (done that before). More embarrassing is not thinking to perform the easiest test of all category theory, F(0) = 0. And most embarrassing is thinking that Mike could have overlooked such an easy example. Sorry, Mike! Vaughan Michael Barr wrote:

Actually, F isn't even a functor. The unique arrow 0 --> Ub has to give a canonical arrow F0 = 1 --> b, which there isn't.