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To: coe@leopard.cs.uidaho.edu (Mike Coe)
Cc: info-hol@ted.cs.uidaho.edu
Subject: Re: help
In-Reply-To: Your message of Mon, 03 May 93 09:59:12 -0700. <9305031659.AA08710@leopard.cs.uidaho.edu>
Date: Mon, 03 May 93 21:36:30 +0000
From: Laurent Thery <Laurent.Thery@cl.cam.ac.uk>
Message-Id: <"swan.cl.cam.:138030:930503213754"@cl.cam.ac.uk>

>> Is there a way prove the following in HOL:
>> ((t-1)+1) = t


The substraction returns only positive numer, so this theorem is false for t=0 

(0-1)+1 = 1

all you can get is the theorem SUB_ADD:

|- !m n. n <= m ==> ((m - n) + n = m)

--Laurent