1. CEA J., Optimisation: théorie et algorithmes Dunot (1971)
2. COURANT R. and HILBERT D., Methods of Mathematical Physics, Interscience Publishers (1953)
3. DERVIEUX A. and PALMERIO B., Thèse de l'Université de Nice
4. DIEUDONNE J. Calcul infinitésimal Hermann (1968)
5. GARABEDIAN P.R. and SCHIFFER M., Variational problems in the theory of elliptic partial differential equations. J. of rat.mech. and analys. p. 137–171 (1953)