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       ETAI NEWSLETTER ON  REASONING ABOUT ACTIONS AND CHANGE        
Issue 97004             Editor: Erik Sandewall             29.9.1997
Back issues available at http://www.ida.liu.se/ext/etai/actions/njl/
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                    *********  DEBATE  *********


  ---  DISCUSSION WITH WOLFGANG BIBEL ABOUT HIS IJCAI LECTURE  ---


FROM: Wolfgang Bibel (answer to Marc Friedman)

> Oh.  Maybe I said it wrong.  I meant that if there are synchronic
> rules, and transition rules, represented in your talk by two
> different kinds of implication arrows, then there are two different
> mechanisms -- one which limits each proposition to use in a single
> connection, and one which does not.

But then - what should be the problem with this technical change in the
syntactic characterization of valid formulas which reflects our semantic
use of (two different) implications?

FROM: Patrick Hayes

I'm surprised to read that any theorem-prover has solved the frame problem,
since the FP is a problem in representation, not in theorem-proving, and
has nothing particularly to do with how deductions are processed. It is
also rather surprising to read that some specialised logic has solved the
FP, since to do so its semantics would have to embody all known and future
causal laws. Could someone briefly explain how a better deductive search
engine, or an exotic logic, can solve a problem in representation?

On what might be a related matter, Bibel claims that ' deduction provides a
generic problem solving mechanism ' (response to Friedman, ETAI Newsletter
on Actions and Change, 26.9.1997). Taken literally, this is clearly false, 
since deduction itself provides no mechanism whatever: one only gets a 
mechanism when one chooses a strategy for performing deductions. For 
example, unification is not imposed by deduction; other strategies for 
instantiating universal variables are possible, computationally ridiculous 
but deductively perfectly valid. So Bibel must be understood as referring 
not to 'deduction' per se, but to a particular deductive strategy, or 
class of deductive strategies. Perhaps in his original lecture (which 
I havn't yet got access to) he tells us which ones they are, but a brief 
summary would be helpful.


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