Return-Path: Return-Path: Received: from ted.cs.uidaho.edu by swan.cl.cam.ac.uk with SMTP (PP-6.0) id <16112-0@swan.cl.cam.ac.uk>; Wed, 15 Jan 1992 13:20:28 +0000 Received: by ted.cs.uidaho.edu.cs.uidaho.edu (16.6/1.34) id AA03595; Wed, 15 Jan 92 05:12:03 -0800 Sender: info-hol-request@edu.uidaho.cs.ted Errors-To: info-hol-request@edu.uidaho.cs.ted Received: from swan.cl.cam.ac.uk by ted.cs.uidaho.edu.cs.uidaho.edu (16.6/1.34) id AA03591; Wed, 15 Jan 92 05:10:58 -0800 Received: from guillemot.cl.cam.ac.uk by swan.cl.cam.ac.uk with SMTP (PP-6.0) to cl id <15960-0@swan.cl.cam.ac.uk>; Wed, 15 Jan 1992 13:12:08 +0000 To: info-hol@edu.uidaho.cs.ted Cc: chou@edu.ucla.cs Subject: Re: Why sets? Date: Wed, 15 Jan 92 13:11:53 +0000 From: Tom.Melham@uk.ac.cam.cl Message-Id: <"swan.cl.ca.987:15.00.92.13.12.26"@cl.cam.ac.uk> Ching-Tsun asks: > I was browsing through library "sets" and this occurred to me: > Why do we need sets at all? Why can't we just use the predicates? > What is the advantage of having a new type (*)set? And when should > I use (*)set and when should I use (* -> bool)? As David pointed out, some people prefer to make distinctions between object to be regarded as sets and functions. For those who would rather work directly with *->bool, there is the library pred_sets. Incidentally, I intend to rewrite pred_sets to make it parallel the library sets, which is the most developed of the set theory libraries. If anyone strongly objects to this, please post me as soon as possible, as I intend to do this soon. Another point: there is an almost finished (i.e. needs 1 day's work) full manual for the sets library. This will be released with version 2.01, but anyone who wants it earlier can contact me. Tom