AGRICULTURE - MONETARY COMPENSATORY AMOUNTS - DETERMINATION - DERIVED PRODUCTS - COMMISSION REGULATION NO 2140/79 , AS AMENDED BY REGULATION NO 1541/80 - INVALIDITY QUESTIONS SUBMITTED FOR A PRELIMINARY RULING - ASSESSMENT OF VALIDITY - DECLARATION THAT A REGULATION IS INVALID - EFFECTS - TEMPORAL LIMITATION ( EEC TREATY , ART . 174 , SECOND PARAGRAPH , AND ART . 177 )