43As regards checks to verify compliance with the financial obligations of beneficiaries of assistance, Article 23 of Regulation No 4253/88, as amended, entitled ‘Financial control’, institutes a system of close cooperation between the Commission and the Member States (see, with respect to, e.g., the European Social Fund, Case T-126/97Sonasa v Commission [1999] ECR II-2793, paragraph 52 and the case-law cited).