Re: NULLs: theoretical problems?

From: V.J. Kumar <vjkmail_at_gmail.com>
Date: Mon, 20 Aug 2007 01:48:06 +0200 (CEST)
Message-ID: <Xns9991C97388F07vdghher@194.177.96.26>

Jan Hidders <hidders_at_gmail.com> wrote in news:1187555898.287393.128980 @a39g2000hsc.googlegroups.com:  

> Such a construct also makes clear how the rules of logic can or cannot
> be applied. For example, what now looks at first sight like a
> tautology, namely "t.a < 5 or t.a >= 5", would then look like either
> "(DEF t.a : t.a < 5) OR (DEF t.a : t.a >= 5)" or "DEF t.a : (t.a < 5
> OR t.a >=5)". Both are equivalent with "DEF t.a : TRUE" but not with
> "TRUE". The logical rules for reasoning with this construct are not
> that difficult to see, and it avoids something like 3VL.
>
> -- Jan Hidders
>

I wonder what the truth tables for 'AND' and 'OR' would look like with the DEF operator. Could you show those tables ? Something like:

x y AND

---

defined
0 0 0
1 0 0
0 1 0
1 1 1
undefined

u 0 ?
u 1 ?
u u ?
0 u ?
1 u ?

Received on Sun Aug 19 2007 - 18:48:06 CDT