Re: A different definition of MINUS, Part 3

From: Bob Badour <bbadour_at_pei.sympatico.ca>
Date: Sun, 21 Dec 2008 21:34:37 -0400
Message-ID: <494eeeaf$0$5498$9a566e8b_at_news.aliant.net>


paul c wrote:

> Bob Badour wrote:
>

>> vadimtro_at_gmail.com wrote:

>
> ...
>
>>> Projection, is inner union in RL terms. Well, I don't see how to
>>> represent inner union in terms of other operations:-(
>>
>>
>> Sigh. One of these days, I really do have to take the time to better 
>> understand the RL. Projection, to me, doesn't seem like any sort of 
>> union.

>
> From the formal definition of <OR> (page 14),
>
> Let s be r1 <OR> r2. It is required that if <A,T1> in Hr1 and
> <A,T2> in Hr2, then T1 = T2.
> Hs = Hr1 union Hr2
> Bs = { ts : exists tr1 exists tr2
> ( ( tr1 in Br1 or tr2 in Br2 ) and
> ts = tr1 union tr2 ) }
>
> If the '<OR>' is changed to say, '<INNER_OR>', and the third and last
> lines changed to read 'intersect' instead of 'union', wouldn't that be
> equivalent to RL inner union?

I assume you must be asking Vadim because you lost me at page 14. lol Received on Mon Dec 22 2008 - 02:34:37 CET

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