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From: ruben safir <ruben@mrbrklyn.com>
Newsgroups: comp.databases.theory
Subject: Re: relational algrabra division?
Date: Fri, 12 Dec 2014 02:33:22 -0500
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On 12/11/2014 09:13 PM, James K. Lowden wrote:
>> > (e) Retrieve the names of employees who work on every project
> That kind!  


in deed.  With enough scotch I can understand this

There is this line in the text about division :(

The DIVISION operation can be expressed as a sequence of π, ×, and –
operations as
follows:
T1 ← πY(R)
T2 ← πY((S × T1) – R)
T ← T1 – T2


 tried this and go some insite but it is still just magic