++++ 1 . PRELIMINARY QUESTIONS - INTERPRETATION - TEMPORAL EFFECTS OF JUDGMENTS BY WAY OF INTERPRETATION - RETROACTIVE EFFECT - LIMITS - LEGAL CERTAINTY - DISCRETION OF THE COURT IN THE PRELIMINARY RULING ITSELF - SUBSEQUENT RESTRICTION - NOT PERMISSIBLE ( EEC TREATY, ART . 177 ) 2 . COMMUNITY LAW - PRINCIPLES - EQUAL TREATMENT - DISCRIMINATION ON GROUNDS OF NATIONALITY - VOCATIONAL TRAINING OFFERED IN ONE MEMBER STATE - REGISTRATION FEE OR "MINERVAL" CHARGED EXCLUSIVELY TO NATIONALS OF OTHER MEMBER STATES - PROHIBITED - ESTABLISHED IN A PRELIMINARY RULING - INTERPRETATION APPLICABLE TO APPLICATIONS FOR ADMISSION TO VOCATIONAL TRAINING COURSES PRIOR TO THE PRELIMINARY RULING ( EEC TREATY, ARTS 7 AND 177 ) 3 . COMMUNITY LAW - DIRECT EFFECT - IMPOSITION OF A REGISTRATION FEE FOR VOCATIONAL TRAINING COURSES INFRINGING THE PROHIBITION OF DISCRIMINATION ON GROUNDS OF NATIONALITY - REPAYMENT - PROCEDURES - APPLICATION OF NATIONAL LAW - LIMITS ( EEC TREATY, ART . 7 )