++++ Tax provisions - Harmonization of laws - Turnover tax - Common system of value-added tax - Exemptions provided for in the Sixth Directive - Exemption for temporary importation - Temporary importation by a frontier worker, for business and private use, of a motor vehicle belonging to his employer - Levying of tax - Not permissible ( Council Directive 77/388, Art . 14 ( 1 ) ( c ) )