1. Arnold, D. N. Discretization by finite elements of a model parameter dependent problem. Numer. Math. 37 (1981), no. 3, 405–421.
2. Bathe, K. J. Finite Element Procedures, Prentice Hall, 1996.
3. Braess, D. Finite elements. Theory, fast solvers, an d applications in solid mechanics. Cambridge University Press, Cambridge, 1997.
4. Texts in Applied Mathematics;SC Brenner,1994
5. Brezzi, F. On the existence, uniqueness and approximation of saddle-point problems arising from Lagrangian multipliers. Rev. Française Automat. Informat. Recherche Opérationnelle Sér. Rouge 8 (1974), no. R-2, 129–151.