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    ELECTRONIC NEWSLETTER ON  REASONING ABOUT ACTIONS AND CHANGE        
Issue 98070             Editor: Erik Sandewall             17.9.1998
Back issues available at http://www.ida.liu.se/ext/etai/actions/njl/
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                    *********  TODAY  *********

Today, we feature two additional questions by Paulo Edouardo Santos to
Murray Shanahan re his ETAI submitted article.


              *********  ETAI PUBLICATIONS  *********

            ---  DISCUSSION ABOUT RECEIVED ARTICLES  ---

The following debate contributions (questions, answers, or comments)
have been received for articles that have been submitted to the ETAI and
which are presently subject of discussion. To see the full context,
for example, to see the question that a given answer refers to, or to
see the article itself or its summary, please use the web-page version 
of this Newsletter.

        ========================================================
        |  AUTHOR: Murray Shanahan
        |  TITLE:  A Logical Account of the Common Sense Informatic 
        |          Situation for a Mobile Robot
        |  PAPER:  http://www.dcs.qmw.ac.uk/~mps/robotics_long.ps.Z
        |  REVIEW: http://www.ida.liu.se/ext/etai/received/actions/010/aip.html
        ========================================================

--------------------------------------------------------
|  FROM: Paulo Eduoardo Santos
--------------------------------------------------------

Dear Murray Shanahan,

As you suggested, I am sending the following questions to the ETAI:

1. On page 5 we read the definition of the following circumscription
policy:

> Given a conjunction of Happens and Initially formulae N, a conjunction
> of Initiates, Terminates and Releases formulae E (...), we are
> interested in :
> 
>    CIRC[N; Happens]\wedge CIRC[E;Initiates, Terminate, Releases]\wedge
>       U\wedge EC.

My question is: Why didn't you circumscribe Initially and Happens in
parallel in the first conjunctive term of the expression above (since we
should expect to have, as true in the time 0, only the explicitly stated
facts and nothing else.)? 


2. The second question concerns the same subject:
On page 9 we have the predicate AbSpace defined in terms of Initially:

AbSpace(w) <- Initially(Occupies(w,g))

Further on we read:

> The predicate AbSpace needs to be minimised, with Initially allowed to
> vary. 

The circumscription policy w.r.t. this idea is described
on the top of page 10 :

   CIRC[O\ wedge M; AbSpace; Initially] \wedge ...

Question:  Why do we have to circumscribe Abspace letting Initially
vary , and not circumscribe only Initially (or both Initially and
Abspace)?

Cheers,

Paulo


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