1. K.-J. Bathe and E. L. Wilson,Numerical Methods in Finite Element Analysis. Prentice-Hall, Englewood Cliffs, 1976.
2. H. Berestycki and H. Brezis, Sur certains problèmes de frontière libre. C. R. Acad. Sci. paris, Sér. A,283 (1976), 1091–1094.
3. H. Berestycki, E. Fernandez Cara and R. Glowinski, A numerical study of some questions in vortex rings theory. Rapports de Recherche. INRIA, No. 116, 1982.
4. P. G. Ciarlet,The Finite Element Method for Elliptic Problems. North-Holland, Amsterdam, 1978.
5. P. G. Ciarlet and P.-A. Raviart, Maximum principle and uniform convergence for the finite element method. Comput. Methods Appl. Mech. Engrg.,2 (1973), 17–31.