6. References

In this dossier, we have followed our book very closely (especially in the first three paragraphs). Numerous books on the subject exist, and we particularly recommend the following (precise references to works not mentioned in this bibliography can be found at ).

• For classic methods: Akhiezer , Bliss , Bolza , Carathéodory , Cesari , Courant , Courant-Hilbert , Gelfand-Fomin , Giaquinta-Hildebrandt , Goldstine, Hadamard, Hestenes, Pars, Troutman and Weinstock.

• For direct methods, non-convex problems, minimal surfaces or isoperimetric inequality: Bandle, Berger, Buttazzo,...