Re: constraints in algebra instead of calculus

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?

-- 
Jon