1. Blum E, Oettli W (1976) The principle of feasible directions for nonlinear approximants and infinitely many constraints. In: Symposia Mathematica, Vol 19, pp 91–101. Istituto Nazionale di Alta Matematica, Roma
2. Jahn J (1986) Mathematical Vector Optimization in Partially Ordered Linear Spaces. Peter Lang, Frankfurt/Main
3. Tuy H, Oettli W (1994) On necessary and sufficient conditions for global optimality. Revista de Matemáticas Aplicadas 15:39–41
4. Wanka G (1994) Kolmogorov-conditions for vectorial approximation problems. OR Spektrum 16:53–58
5. Zowe J (1976) Konvexe Funktionen und konvexe Dualitätstheorie in geordneten Vektorräumen. Habilitationsschrift, Universität Würzburg