On Wed, Jun 22, 2011 at 2:19 PM, wren ng thornton <w...@freegeek.org> wrote: >>> [1] modulo the A:+:A ~ A issue. > > Oops, I should've said A:*:A there. > >> That issue is exactly my concern, though, and it seems a bit too >> thorny to handwave aside. > > Indeed. If we have A:*:A ~ A, then A:*:A is not a categorical product. (...)
Thank you, that clarified my intuitive sense of why it didn't seem to work. The same argument, with arrows flipped appropriately, would apply to a hypothetical coproduct where A :+: A ~ A, wouldn't it? > Disjoint pairs are sufficient; they needn't be ordered. All we need is > that they are "tagged" in the same way that disjoint unions are, so that > we can distinguish the components of A*A. Oh. Yes, of course, I probably knew that. I think confused myself by habitually calling the components "fst" and "snd". Sigh. - C. _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
