Re: Unique Keys
From: Paul <paul_at_test.com>
Date: Sun, 28 Nov 2004 00:11:49 +0000
Message-ID: <41a917c5$0$43595$ed2e19e4_at_ptn-nntp-reader04.plus.net>
Date: Sun, 28 Nov 2004 00:11:49 +0000
Message-ID: <41a917c5$0$43595$ed2e19e4_at_ptn-nntp-reader04.plus.net>
Kenneth Downs wrote:
> In another subthread of this thread I suggested a datatype interval,
> composed of an ordered pair of any two values of the same base type, (a,b)
> where a<=b. Equality could then be defined as:
>
> where x = (a,b)
> and y = (c,d)
>
> x = y iff (a <= c <= b) OR (a <= d <= b)
But as Mikito pointed out, for equality you want the property that:
if x=y and y=z, then x=z.
And this isn't true in this case.
Also, what about the case where the interval (c,d) totally overlaps the
interval (a,b)? e.g. x = (2,3) and y = (1,4)?
Paul.