1 . COMMUNITY LAW - PRINCIPLES - LEGAL CERTAINTY 2 . TAX PROVISIONS - HARMONIZATION OF LAWS - TURNOVER TAXES - COMMON SYSTEM OF VALUE-ADDED TAX - EXEMPTIONS PROVIDED FOR IN THE SIXTH DIRECTIVE - EXEMPTION FOR TRANSACTIONS CONSISTING OF THE NEGOTIATION OF CREDIT - POSSIBILITY OF INDIVIDUALS ' RELYING ON THE APPROPRIATE PROVISION IN THE EVENT OF THE DIRECTIVE ' S NOT BEING IMPLEMENTED - EXTENSION OF THE PERIOD FOR TRANSPOSING THE DIRECTIVE INTO NATIONAL LAW - EFFECTS ( COUNCIL DIRECTIVES 77/388 , ART . 13 B ( D ) 1 AND 78/583 , ART . 1 )