Re: A proposal of "sorts"

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Message-id: <199401072256.AA17242@dante.cs.uiuc.edu>
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Date: Fri, 7 Jan 1994 17:01:19 +0000
To: Tomas Uribe <uribe@CS.Stanford.EDU>
From: phayes@cs.uiuc.edu
Subject: Re: A proposal of "sorts"
Cc: Interlingua-working-group@ISI.EDU

....
>
>>why not just have instead
>>        SortOf(?x,?y) => (SortOf(?y,S))  ?
>
>OK. 
>

Quick comment on the above: it allows 'empty' sorts which have no
exemplars. Do you want that, or should you insist that

        (SortOf(?y,S)) => (exist ?x)(SortOf(?x,?y))

or at least that

           (and (SortOf(?y,S)
                (SortOf(?z,S)
                (forall ?x)((and(not SortOf(?x,?y)
                                (not SortOf(?x,?z)) ) => ?y=?z

in order to make the empty sort unique? If not, then sorts will need a
nonextensional semantics.

Pat


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