Re: constraints in algebra instead of calculus

From: paul c <toledobythesea_at_oohay.ac>
Date: Sun, 17 Jun 2007 17:50:54 GMT
Message-ID: <2wedi.34960$1i1.9012@pd7urf3no>

Jon Heggland 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) }) }.
>
>

>>(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?

It's looking to me now that you are right about WRAP and that I too was confusing it with GROUP, so maybe the constraint should look like:

R{B} WRAP {B} as gB = R{B} GROUP {B} as gB,

also that as far as TTM/Tutorial D is concerned, Bob B was right about

R{B} GROUP {B} as gB = (R GROUP {B} as gB} {gB} being a tautology.

p (waiting to be corrected for the umpteenth time!) Received on Sun Jun 17 2007 - 12:50:54 CDT