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    ELECTRONIC NEWSLETTER ON  REASONING ABOUT ACTIONS AND CHANGE        
Issue 97021             Editor: Erik Sandewall             12.11.1997
Back issues available at http://www.ida.liu.se/ext/etai/actions/njl/
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              *********  ETAI PUBLICATIONS  *********

            ---  DISCUSSION ABOUT RECEIVED ARTICLES  ---

The following debate contributions (questions, answers, or comments)
have been received for articles that have been received by 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: Antonis Kakas and Rob Miller
        |  TITLE:  Reasoning about Actions, Narratives and Ramification
        ========================================================

--------------------------------------------------------
|  FROM: The Authors
|  TO:   Tom Costello
--------------------------------------------------------

Hi Tom,

You wrote:
> In Antonis and Rob's case they lack truth conditions for some
> of their propositions, and worse, it seems that it is not even
> possible to define truth conditions.

As we said in our original answer to your question, it's trivial
to extend the semantics of the Language E to include truth
conditions for h- and c-propositions, but superfluous (to the
main themes of the present and previous papers).  However,
for the record, you can do this by defining an interpretation
as a tuple <H,J,K>.  H is as before, J is a function from
Actions x Time-points to {true,false}, and K is a function
from Actions x Fluent-literals x 2^Fluent-literals to
{true,false}. The definition of a model is exactly as before
(Definition 9), with the additional conditions:
(5) J(A,T)=true iff "A happens-at T" is in D, and
(6) K(A,L,C)=true iff either "A initiates L when C" is in D
or L=-F and "A terminates F when C" is in D. But this
doesn't really add much insight; you just get that D entails
a given h- or c-proposition iff the proposition is in D. Of
course, for other extensions of E it might become
worthwhile complicating the structure of an interpretation
in this way. (Similarly for r-propositions.) Again, you might
find Van Belleghem, Deneker and Dupre interesting in this
respect.

Rob and Tony

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