Quoth V.J. Kumar:
> Jan Hidders <hidders_at_gmail.com> wrote in
> news:1188037788.486939.308150_at_i38g2000prf.googlegroups.com:
>
>> On 25 aug, 02:13, "V.J. Kumar" <vjkm..._at_gmail.com> wrote:
>>> 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 ?
>
> 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 ?
I believe the point is that if x is not defined, it makes no sense to
evaluate f(x) (because we are using 2VL, and every expression /must/
have a value). In practical terms, you have to evaluate def(x) first,
and only consider f(x) if def(x) is indeed TRUE. Contrast this with an
ordinary AND expression, where it doesn't matter which term you evaluate
first. Also, this makes it irrelevant what tautologies or contradictions
may be present in f(x) when x is undefined---they are ignored regardless.
--
Jon
Received on Sun Aug 26 2007 - 03:12:25 CDT
