[2] J. L. Lions: 
Quelques méthodes de résolution des problèmes aux limites non linéaires. Dunod, Gauthier-Villars, Paris 1969. 
MR 0259693 | 
Zbl 0189.40603[3] U. Mosco: Convergence of Solutions of Variational Inequalities; Theory and Applications of Monotone Operators. Proceedings of a NATO Advanced Study Institute held in Venice, Italy, June 17-30, 1968.