I've never thought of one being shorthand for the other, really.
Since they are logically equivalent (in my interpretation) I don't really
care which one we regard as more primitive.
On Fri, Apr 18, 2008 at 9:26 AM, Martin Sulzmann
Lennart Augustsson wrote:
To reuse a favorite word, I think that any implementation that distinguishes 'a -> b, a -> c' from 'a -> b c' is broken. :) It does not implement FD, but something else. Maybe this something else is useful, but if one of the forms is strictly more powerful than the other then I don't see why you would ever want the less powerful one.
Do you have any good examples, besides the contrived one
class D a b c | a -> b c
instance D a b b => D [a] [b] [b]
where we want to have the more powerful form of multi-range FDs?
Fixing the problem who mention is easy. After all, we know how to derive improvement for multi-range FDs. But it seems harder to find agreement whether multi-range FDs are short-hands for single-range FDs, or certain single-range FDs, eg a -> b and a -> c, are shorthands for more powerful multi-range FDs a -> b c. I clearly prefer the latter, ie have a more powerful form of FDs.
Martin