1. Case C-555/07, Kücükdeveci, 2010 E.C.R. I-0000, para. 23. As to the limits, see Case C-299/95, Kremzow, 1997 E.C.R. I-2629, para. 19.
2. Cases 7/56 and 3–7/57, Algera et al. v. Common Assembly, 1957 E.C.R. (English special edn.) 39, 54 et seq‥
3. On the various sources of this multi-level body of law, see European Migration Law 35 (P. Boeles et al, eds., 2009).
4. Council Directive 2004/114/EC of 13 December 2004 on the conditions of admission of third-country nationals for the purposes of studies, pupil exchange, unremunerated training or voluntary service, O.J. 2004 L 375/12.