1 . FREE MOVEMENT OF GOODS - CUSTOMS DUTIES - CHARGES HAVING AN EQUIVALENT EFFECT - PROHIBITION - DIRECT EFFECT - CONSEQUENCES ( EEC TREATY , ART . 13 ( 2 )) 2 . REFERENCES FOR A PRELIMINARY RULING - INTERPRETATION - EFFECTS IN TIME OF INTERPRETATIVE JUDGMENTS - RETROACTIVE EFFECT - LIMITS - LEGAL CERTAINTY ( EEC TREATY , ART . 177 ) 3 . COMMUNITY LAW - DIRECT EFFECT - INDIVIDUAL RIGHTS - PROTECTION BY NATIONAL COURTS - PRINCIPLE OF CO-OPERATION ( EEC TREATY , ART . 5 ) 4 . COMMUNITY LAW - DIRECT EFFECT - NATIONAL CHARGES INCOMPATIBLE WITH COMMUNITY LAW - CONDITIONS FOR RECOVERY - APPLICATION OF NATIONAL LAW - CONDITIONS - TAKING INTO ACCOUNT POSSIBLE PASSING ON OF CHARGE - PERMISSIBILITY 5 . AIDS GRANTED BY STATES - CONCEPT - REPAYMENT OF CHARGES UNDULY LEVIED - EXCLUSION ( EEC TREATY , ART . 92 ( 1 ))