Re: A different definition of MINUS, Part 3

On Dec 21, 11:53 am, Bob Badour <bbad..._at_pei.sympatico.ca> wrote:
> vadim..._at_gmail.com wrote:
> > On Dec 21, 11:36 am, vadim..._at_gmail.com wrote:
>
> >>x + y = ((x ^ x)' ^ (y ^ y)')'.
> >>... is tough...
>
> > Actually, easy. The right side simplifies to
>
> > x + y = (x' ^ y')'.
>
> > Applying double negation (provable in RL), we get
>
> > (x+y)' = x' ^ y'.
>
> > De Morgan, which is again provable in RL. Amazing.
>
> Why are you amazed?

Two reasons:
1. Relational Algebra is a weaker system than boolean algebra. Therefore there is no reason to expect BA properties to carry over. 2. All RA operation, not just three can be reduced to a single one. Here is my worksheet:

Join, is <AND>. It is representable in terms of Sheffer stroke. Projection, is inner union in RL terms. Well, I don't see how to represent inner union in terms of other operations:-( Received on Sun Dec 21 2008 - 21:40:12 CET