17A judgment delivered on a reference for a preliminary ruling is such as to have effects on legal relationships which arose before its delivery. It follows, in particular, that a rule of Community law so interpreted must be applied by an administrative body within the sphere of its competence even to legal relationships which arose and were formed before delivery of the Court's judgment ruling on the question referred to it (see, to this effect, Kühne & Heitz, cited above, paragraph 22). In the absence of Community rules on applications for the repayment of taxes, it is for the domestic legal system of each Member State to lay down the conditions under which such applications may be made; those conditions must observe the principles of equivalence and effectiveness, that is to say, they must not be less favourable than those relating to similar claims founded on provisions of domestic law or framed so as to render virtually impossible the exercise of rights conferred by the Community legal order (see, to this effect, Case 199/82 San Giorgio [1983] ECR 3595, paragraph 12, and Case C-147/01 Weber's Wine World and Others [2003] ECR I-11365, paragraph 103).
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