Re: more closed-world chatter

From: Vadim Tropashko <vadimtro_invalid_at_yahoo.com>
Date: 10 May 2007 09:55:45 -0700
Message-ID: <1178816145.292150.231080@h2g2000hsg.googlegroups.com>

> > Is generalized minus the same as semiminus?
>
> I suggest semijoin

eh, antijoin

> as a generalized minus. The generalized Date
> identity is:
>
> (A /\ B) \/ (A /\ 00) = A \ (A \ B)
>
> where /\ is join, \/ is generalized union, and \ is antijoin.

The reason why this formula is fascinating is that setting B=11 reduces it to

(A /\ 11) \/ (A /\ 00) = A

the "fundamental" decomposition identity (Proposition 1 from http://arxiv.org/abs/cs/0603044). Received on Thu May 10 2007 - 11:55:45 CDT