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*                       Ecole Normale Supe'rieure                   *
*                                                                   *
*                              Se'minaire                           *
*                SEMANTIQUE ET INTERPRETATION ABSTRAITE             *
*                              P. Cousot                            *
*                                                                   *
*                        Vendredi, 14h--16h                         *
*                 Salle W, 4e`me e'tage, toits du DMA               *
*                  DI  ENS  45 rue d'Ulm  75005 Paris               *
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*** Vendredi 11 f'evrier 1994 *** Salle M6, 11h--12h ****************

A Semantic Framework for Positive Logic Programs

Giorgio LEVI (Pisa)

Re'sume' : We consider a framework for defining various (concrete 
and abstract) semantics which model different observables for 
positive logic programs. All the semantics can be obtained by a 
suitable abstraction of a collecting semantics which is essentially
the set of resultants for most general atomic goals. We have a set 
of general properties (AND-compositionality, equivalent bottom-up 
definition, OR-compositionality, etc.) which are inherited by all 
the semantics, if the abstraction satisfies suitable properties.

*** Vendredi 11 f'evrier 1994 *** Salle W, 4e`me e'tage, 14h--16h ***

Coordination for Concurrent Programming

Sandra HOLZBACHER (LIX)

Re'sume' : For both reactive and transformational applications, 
concurrent programming allows to write more efficient programs than 
sequential programming. Concurrent programming remains a fairly new 
area in which program development is still a complex and expensive 
process.

   The goal of this work is a programming environment that reduces 
the drawbacks of concurrent programming while it exploits its 
advantages and supports reusability. The environment will be based on
the separation of the computation and coordination elements of 
concurrent programming.

   This talk will first define these two elements. Second, it will 
explain the advantages that can be expected from a good separation of
the computation and coordination elements by a programming environment.
Third, it will discuss different kinds of separation with examples. 
Finally, the talk will provide an outline of the foreseen future work.

*** Vendredi 18 f'evrier 1994 ***************************************

\`A propos du probl\`eme SAT et de la proc\'edure de Davis et Putnam

Antoine RAUZY (LABRI, Bordeaux)

Re'sume' : Le probl\`eme SAT (SATisfiabili\'e d'un ensemble de clauses
propositionnelles) est l'un des probl\`emes clefs en d\'emonstration
automatique. Il est le probl\`eme NP-complet de r\'ef\'erence. Le but
de cet expos\'e est de faire le point sur quelques r\'esultats
r\'ecents sur ce sujet. Ces r\'esultats sont de deux ordres: on 
\'etudiera d'une part la complexit\'e de la proc\'edure de Davis et
Putnam sur les restrictions polynomiales connues du probl\`eme SAT.
La proc\'edure de Davis et Putnam est sans doute l'algorithme de
d\'ecision le plus simple que l'on puisse imaginer pour SAT. C'est
aussi le plus efficace en pratique. Il est donc int\'eressant 
d'\'etudier son comportement vis \`a vis d'algorithmes sp\'ecialis\'es
pour la r\'esolution d'un sous-probl\`eme particulier de SAT. D'autre
part, on montrera les r\'esultats d'\'etudes statistiques du
probl\`eme SAT. On discutera en particulier de la possibilit\'e
de g\'en\'erer al\'eatoirement des instances difficiles de
ce probl\`eme.

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Pour recevoir l'annonce par courrier electronique: cousot@di.ens.fr
WWW: http://www.di.ens.fr/~cousot/annonceseminaire.shtml
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