++++ Agriculture - Common organization of the markets - Cereals - Co-responsibility levy - Operations subject to the levy - Placing of products on the market - Concept - Reimbursement of the levy collected in respect of processing carried out by a third party on account of a producer who uses the products on his own holding - Scope - Producers who buy back products processed from cereals previously sold by them to the processors - Exclusion ( Commission Regulations Nos 2040/86, Art . 1(2 ), second subparagraph, as amended by Regulation No 2572/86, 1432/88, Art . 1(2 ), and 3779/88, Art . 1(1 ) )