Re: Notions of Type

From: paul c <toledobythesea_at_oohay.ac>
Date: Fri, 18 Aug 2006 00:43:50 GMT
Message-ID: <a38Fg.416358$iF6.240557@pd7tw2no>

Aloha Kakuikanu wrote:
> paul c wrote:

>> Aloha Kakuikanu wrote:
>>> Keith H Duggar wrote:
>>>> Marshall wrote:
>>>>> Very true. Of the various relational operators that have
>>>>> been identified over the years, only a few, like union,
>>>>> are really algebraic.
>>> Except that union applies to relations of the same arity only.
>> I thought that was only a practical restriction, ie., in theory, any
>> relations can be unioned?

>
> Which theory:-?
>
> In classic RA they aren't.
>
> In D&D algebra they are. In relational lattice they are too.
>

I guess I meant D&D. Still, I thought the 'classic' version must have to allow for different headers in theory, even if not in practice, otherwise axioms like de Morgan's laws wouldn't be true. (When I read about the lattice's union, I was puzzled for the same reason.)

p Received on Thu Aug 17 2006 - 19:43:50 CDT