SOVEREIGNTY IN BYZANTIUM AND IN THE WEST FROM THE 8TH-CENTURY TO THE 10TH-CENTURY - PROCEEDINGS OF THE INTERNATIONAL COLLOQUY ORGANIZED BY THE INSTITUT-DES-HAUTES-ETUDES IN BELGIUM IN COLLABORATION WITH THE DEPARTMENT-OF-HISTORY AT THE UNIVERSITE-LIBRE-DE-BRUXELLES, (27-28-APRIL, 1990) - FRENCH - DIERKENS,A, SANSTERRE,JM