TAX PROVISIONS - HARMONIZATION OF LAWS - TURNOVER TAX - COMMON SYSTEM OF VALUE-ADDED TAX - EXEMPTIONS PROVIDED FOR IN THE SIXTH DIRECTIVE - EXEMPTION FOR CREDIT NEGOTIATION TRANSACTIONS - POSSIBILITY OF INDIVIDUALS ' RELYING ON THE APPROPRIATE PROVISION IN THE EVENT OF THE DIRECTIVE ' S NOT BEING IMPLEMENTED - CONDITIONS ( COUNCIL DIRECTIVE 77/388 , ART . 13 B ( D ) 1 .)