On Dec 5, 2007 12:30 PM, Andrew Coppin <[EMAIL PROTECTED]> wrote: > > Luke Palmer wrote: > > On Dec 5, 2007 11:56 AM, Andrew Coppin <[EMAIL PROTECTED]> wrote: > > > >> I was merely noting that questions of the form "is X decidable?" are > >> usually undecidable. (It's as if God himself wants to tease us...) > >> > > > > I take issue with your definition of "usually" then. > > > > Whenever "X is decidable" is undecidable, "'X is decidable' is decidable' is > > decidable, namely false. So there are at least as many decidable sentences > > of the form "X is decidable" as there are undecidable ones. > > > > Ouch... my head hurts. > > OK, well how about I rephrase it as "most 'interesting' questions about > decidability tend to be undecidable" and we call it quits? ;-)
Nah, I was just performing a slight-of-hand on you. Basically by saying "X is decidable" is undecidable, you were implying you could prove it. Which you usually can't. Well, rather, which you usually don't know if you can... Luke _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
