1. Alexandroff, P., Hopf, H.: Topologie. Chelsea Publishing Company, New York (1972)
2. Clarke, FH.: Optimization and Nonsmooth Analysis. Les publications CRM, Université de Montréal (1989)
3. Deimling, K.: Nonlinear Functional Analysis. Springer, New York (1985)
4. Demyanov, VF. Rubinov, AM.: Quasidifferential Calculus. Optimization Software, Inc., New York (1986)
5. Halkin, H.: Implicit functions and optimization problems without continuous differentiability of the data. SIAM J. Contr. 12, 229–236 (1974)