AGRICULTURE - COMMON ORGANIZATION OF THE MARKET - CEREALS - PRODUCTS PROCESSED FROM CEREALS AND RICE - EXPORT REFUNDS - AMOUNT OF THE REFUND SUBJECT TO ADJUSTMENT - APPLICATION OF DIFFERENT COEFFICIENTS TO THE REFUND AND TO THE ADJUSTMENT - REGULATIONS NOS 851/79 AND 1309/79 - VALIDITY ( REGULATION NO 2744/75 OF THE COUNCIL , ART . 6 AND ANNEX I ; COMMISSION REGULATIONS NOS 851/79 AND 1309/79 )