# Re: NULLs: theoretical problems?

Date: Sun, 26 Aug 2007 07:21:11 -0000

Message-ID: <1188112871.351486.46330_at_y42g2000hsy.googlegroups.com>

On 25 aug, 16:39, "V.J. Kumar" <vjkm..._at_gmail.com> wrote:

*> Jan Hidders <hidd..._at_gmail.com> wrote innews:1188037788.486939.308150_at_i38g2000prf.googlegroups.com:
**>
**>
**>
*

> > On 25 aug, 02:13, "V.J. Kumar" <vjkm..._at_gmail.com> wrote:

*> >> Jan Hidders <hidd..._at_gmail.com> wrote
**> >> innews:1187998409.227306.271460_at_e9g2000prf.googlegroups.com:
**>
**> >> > On 24 aug, 16:35, "V.J. Kumar" <vjkm..._at_gmail.com> wrote:
**> >> >> You may be right, but then why the formula was not written with
**> >> >> an explicit 'and' ?
**>
**> >> > Because it does not satisify all the logical laws of an AND, so to
**> >> > avoid confusion another notation is used.
**>
**> >> What logical laws of AND are violated when we interpret
**>
**> >> 'def(x):f(x)' as 'def(x) and f(x)' ?
**>
**> > Commutativity and associativity.
**>
**> What "Commutativity" ?
**>
**> Does not 'f(x) and def(x)' evaluate to the same as 'def(x) and f(x)'
**> would where def(x) is interpreted as a definedness predicate ?
*

Assuming that your are working in some 3VL so f(x) is defined, yes, it probably does.

> What "associativity" ?

*>
**> Does not 'def(x) and (x or y)' evaluate to the same as 'def(x) and x or
**> def(x) and y' would where def(x) is interpreted as a definedness
**> predicate ?
*

Yep.

- Jan Hidder