As far as A is concerned, the definition aryl also includes bicyclic systems which consist of a benzene ring fused with a 5- or 6-membered heterocyclic ring as defined above and in turn the5- or 6-membered heterocycles may be fused with a benzene ring.One especially preferred embodiment of the invention is a compound in which A is a difluorobenzodioxolyl group of formula ##STR4##A preferably rep