Re: Types and "join compatibility"

From: Marshall Spight <marshall.spight_at_gmail.com>
Date: 4 Aug 2005 08:22:48 -0700
Message-ID: <1123168968.857958.281820@g44g2000cwa.googlegroups.com>

x wrote:
> "Marshall Spight" <marshall.spight_at_gmail.com> wrote in message
> news:1123082304.749632.295840_at_g44g2000cwa.googlegroups.com...
>
>
> > In the same way:
>
> > Let U = the universal set. U:U
> > M intersect N = N minus (U minus M)
> > type (M intersect N) = type (N minus (U minus M)) =
> > type (M) union (type (U) union type M) =
> > type (M) union (type U) =
> > type (U)
>
> > So the *real* answer is that the static type is the universal set.
>
> Thank you !

My pleasure!

> I had this hunch a couple of years ago, but I didn't try to prove it.
>
> Funny thing this "minus" operator :-)

Yes. As a friend pointed out to me, it's those inverse operations that will screw you up. Multiply is so pleasant, but divide has that nasty zero-trap you have to watch out for.

Marshall Received on Thu Aug 04 2005 - 10:22:48 CDT