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Re: constraints in algebra instead of calculus

From: Jan Hidders <hidders_at_gmail.com>
Date: Sun, 17 Jun 2007 16:38:04 -0700
Message-ID: <1182123484.229004.167360@o61g2000hsh.googlegroups.com>


On 16 jun, 14:22, Jon Heggland <jon.heggl..._at_idi.ntnu.no> wrote:
> Jan Hidders wrote:
> > Assume R = { (A:1, B:2), (A:1, B:3) }
>
> > R{B} = { (B:2}, (B:3) }
> > R1 = R{B} GROUP {B} AS gB = { (gB:{ (B:2} }), (gB:{ (B:3) }) }
>
> Isn't that WRAP, not GROUP? According to (my reading of:) TTM, { (B:2),
> (B:3) } GROUP {B} AS gB = { (gB:{ (B:2), (B:3) }) }.

Ahem, *cough* , you are right, and unfamiliary with TTM is no excuse since the standard nesting operation does the same. That should have been something like:

R1 = (R EXTEND ( RELATION { TUPLE { B B } } AS gB )){ gB }

> > (R GROUP {B} AS gB) = { (A:1, gB:{ (B:2}, (B:3) }) }
> > R2 = (R GROUP {B} AS gB){gB} = { (gB:{ (B:2}, (B:3) }) }
>
> But this is GROUP, not WRAP ... Is this an error, or are you using some
> other definition of GROUP than TTM's?

Here the GROUP is correct.

Received on Sun Jun 17 2007 - 18:38:04 CDT

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