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    ELECTRONIC NEWSLETTER ON  REASONING ABOUT ACTIONS AND CHANGE        
Issue 98074             Editor: Erik Sandewall             1.10.1998
    Back issues available at http://www.ida.liu.se/ext/etai/rac/
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                    *********  TODAY  *********

One more reference article is advertised today, this time by Patrick 
Doherty and his co-workers and describing their language tradition
TAL. Also today, Tom Costello has a question to Graham White regarding 
his article on "Simulation, Ramification, and Linear Logic" that was 
advertised on September 21.



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

                ---  RECEIVED RESEARCH ARTICLES  ---

        ========================================================
        |  AUTHOR: Patrick Doherty, Joakim Gustafsson, Lars Karlsson, 
        |          and Jonas Kvarnström
        |  TITLE:  TAL: Temporal Action Logics Language Specification and 
        |          Tutorial
        |  PAPER:  http://www.ida.liu.se/ext/epa/cis/1998/015/tcover.html
        |          [provisional]
        |  REVIEW: http://www.ida.liu.se/ext/etai/ra/rac/014/
        ========================================================


                             ABSTRACT 

The purpose of this article is to provide a uniform, lightweight language
specification and tutorial for a class of temporal logics for reasoning
about action and change that has been developed by our group during the
period 1994-1998. The class of logics are collected under the name TAL,
an acronym for **Temporal Action Logics**. TAL has its origins
and inspiration in the work with Features and Fluents (FF) by Sandewall,
but has diverged from the methodology and approach through the years. We 
first discuss distinctions and compatibility with FF, move on to the 
lightweight language specification, and then present a tutorial in terms 
of an excursion through the different parts of a relatively complex 
narrative defined using TAL. We conclude with an annotated list of 
published work from our group.

The article tries to strike a reasonable balance between detail and 
readability, making a number of simplifications regarding narrative syntax 
and translation to a base logical language. Full details are available in 
numerous technical reports and articles which are listed in the final 
section of this article.



            ---  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: Graham White
        |  TITLE:  Simulation, Ramification, and Linear Logic
        |  PAPER:  http://www.ep.liu.se/ea/cis/1998/011/
        |  REVIEW: http://www.ida.liu.se/ext/etai/ra/rac/012/
        ========================================================

--------------------------------------------------------
|  FROM: Tom Costello
--------------------------------------------------------

Dear Graham

On page 2 of your article, "Simulation, Ramification, and Linear
Logic" you suggest that effect axioms should have $\Sigma_1$
antecedents and frame axioms $\Pi_1$ antecedents, based on intuitions
concerning locality.  However, some local properties, such as there
being no block in a certain place are expressed as $\Pi_1$ formulas,
not as $\Sigma_1$ formulas, e.g.  $\forall b. \neg at(b,l) $ states
that there is no block at location $l$.

It seems to me that many effect axioms will have preconditions that
say that the effect will occur in certain circumstances, unless there
is something that prevents it.  This is naturally written as a $\Pi_1$
formula. Consider the Blocksworld. One effect axiom there can be
written, 

\[\forall b,l,,s. (\forall b'. \neg On(b', top(b),s)) \land
(\forall b'. \neg On(b',l,s)) \land top(b) \neq l \rightarrow
On(b,l,move(b,l,s)). \]


The left hand side side of this effect axiom is clearly equivalent to
a $\Pi_1$ formula.  It seems that many preconditions will have this
form.  This seems to contradict your intuitions that effect axioms
have $\Sigma_1$ antecedents, and that {\em sufficient} conditions can
be written in $\Sigma_1$.

Yours,  

Tom Costello

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