Supplies and intermediation services relating to directories and periodical publications other than those mentioned in article 298 septies published by public authorities and their public administrative establishments, as well as by not-for-profit organisations, are exempt on condition, firstly, that advertisements and publicity never cover more than two thirds of the surface area of these periodicals or directories, and secondly, that the total of advertisements or publicity from a single advertiser is never, in any one year, greater than one tenth of the total surface area of the issues published during that year.