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Re: x*x-1=0

From: Vadim Tropashko <vadimtro_at_yahoo.com>
Date: Wed, 24 Jan 2001 18:38:11 GMT
Message-ID: <94n7ei$iad$1@nnrp1.deja.com>

In article <94mhpf$jdh$1_at_news.tue.nl>,
  hidders_at_win.tue.nl (Jan Hidders) wrote:
> Note that if you have ordered tuples then the projection is also
 likely
> to be slightly different. If you say PROJ[#1,#2](R) then that will
 mean
> something else than PROJ[#2,#1](R).

What are unordered tuples: sets or bags?

> > I disagree that CP = MULTIPLY, and, in general, that order of
 columns
> > matters. This is why I wanted some congruences on tuples.
>
> You cannot disagree, it is just a matter of definition. :-) And
 whether
> CP = MULTIPLY depends an how you define MULTIPLY and that you didn't
 do
> yet.

Well, I meant definition from Chris Date's textbook. It might look less rigorous than CP defined on tuples, but it captures one important concept that tuple theory is missing -- domains. In this context CP =/= MULTIPLY, right?

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http://www.deja.com/ Received on Wed Jan 24 2001 - 12:38:11 CST

Original text of this message

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