I R I S A I N S T IT U T D E R E C H E R C H E E N IN F O R M A TIQ U E E T S Y S T È M E S A LÉ A T OIR E S P U B L I C A T I O N I N T E R N E N o I R I S A CAMPUS UNIVERSITAIRE DE BEAULIEU - 35042 RENNES CEDEX - FRANCE ISSN 1166-8687 1393 CONDITION-BASED PROTOCOLS FOR SET AGREEMENT PROBLEMS ACHOUR MOSTEFAOUI , SERGIO RAJSBAUM , MICHEL RAYNAL , MATTHIEU ROY