1. H. Attouch, R. Wets. “A convergence theory for saddle functions”. Trans. Amer. Math. Soc., 280 (1983), pp. 1–41.
2. E.J. Balder. “An extension of duality-stability relations to nonconvex optimization problems”. SIAM J. Control Optim., 15 (1977), 329–343.
3. L. Cesari. “Seminormality and upper semicontinuity in optimal control”. J. Opt. Th. Appl., 6 (1970), 114–137.
4. G. Choquet. “Sur les notions de filtre et de grille”. C.R. Ac. Sci. Paris, 224 (1947), 171–173.
5. E. De Giorgi. “Generalized limits in calculus of variations”. In “Topics in Functional Analysis”, Quaderno Scuola Normale Superiore, Pisa (1980–81).