1. Lecture Notes in Economics and Mathematical Systems;K. H. Elster,1985
2. Elster, K. H., andThierfelder, J.,Abstract Cone Approximations and Generalized Differentiability in Nonsmooth Optimization, Optimization, Vol. 19, pp. 315?341, 1988.
3. Elster, K. H., andThierfelder, J.,On Cone Approximations and Generalized Directional Derivatives, Nonsmooth Optimization and Related Topics, Edited by F. H. Clarke, V. F. Demyanov, and F. Giannessi, Plenum Press, New York, pp. 133?154, 1988.
4. Elster, K. H., andThierfelder, J.,Generalized Notions of Directional Derivatives, Research Paper No. 155, Applied Mathematics, Optimization, and Operations Research Section, Department of Mathematics, University of Pisa, 1988.
5. Giorgi, G., andGuerraggio, A.,On the Notion of Tangent Cone in Mathematical Programming, Optimization (to appear).