Re: <OR> predicate?

On 27/09/2010 11:22 AM, Vadim Tropashko wrote:
> On Sep 27, 10:57 am, paul c<toledobythe..._at_oohay.ac> wrote:
...
>> I would think one possible predicate of R<OR> (<NOT> R) would be
>> something like "position Position is occupied OR unoccupied".
>>
>> Seems that an even simpler expression, R<OR> TABLE_DEE, gives the same
>> extension. Is the predicate the same? Or is there a good reason to
>> think instead of the predicate as something like "position Position Exists"?
...
> This assertion (and any other) can be checked in QBQL; here is how:
>
> 1. Translate Tutorial D terms into QBQL:
> TABLE_DEE = R01
> <OR> = _at_v (former "+", see http://vadimtropashko.wordpress.com/relational-programming-with-qbql/udf/)
> <NOT> = _at_' (former "'")
> 2. Write your assertion in QBQL
> x _at_v (x @') = x @v R01.
> 3. Run the program containing this assertion.
>
> QBQL will iterate through all the relations in the database trying to
> find counterexample. In this case it finds none.

Vadim, thank you for going to the trouble to show that, ie., if I'm reading your syntax correctly, it means that R <AND> (<NOT> R) = R <OR> TABLE_DEE, as I thought. Received on Mon Sep 27 2010 - 20:49:57 CEST