Missouri Journal of Mathematical Sciences

Intersection Theorems for Closed Convex Sets and Applications

Hichem Ben-El-Mechaiekh

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A number of landmark existence theorems of nonlinear functional analysis follow in a simple and direct way from the basic separation of convex closed sets in finite dimension via elementary versions of the Knaster-Kuratowski-Mazurkiewicz principle - which we extend to arbitrary topological vector spaces - and a coincidence property for so-called von Neumann relations. The method avoids the use of deeper results of topological essence such as the Brouwer Fixed Point Theorem or the Sperner's Lemma and underlines the crucial role played by convexity. It turns out that the convex KKM Principle is equivalent to the Hahn-Banach Theorem, the Markov-Kakutani Fixed Point Theorem, and the Sion-von Neumann Minimax Principle.

Article information

Missouri J. Math. Sci., Volume 27, Issue 1 (2015), 47-63.

First available in Project Euclid: 3 December 2015

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Mathematical Reviews number (MathSciNet)

Zentralblatt MATH identifier

Primary: 52A07: Convex sets in topological vector spaces [See also 46A55]
Secondary: 32F32: Analytical consequences of geometric convexity (vanishing theorems, etc.) 32F27: Topological consequences of geometric convexity 47H04: Set-valued operators [See also 28B20, 54C60, 58C06] 47H10: Fixed-point theorems [See also 37C25, 54H25, 55M20, 58C30] 47N10: Applications in optimization, convex analysis, mathematical programming, economics

Separation of convex sets intersection theorems convex KKM Theorem fixed points for von Neumann relations coincidence systems of nonlinear inequalities variational inequalities minimization of functionals Markov-Kakutani Fixed Point Theorem Hahn-Banach theorem


Ben-El-Mechaiekh, Hichem. Intersection Theorems for Closed Convex Sets and Applications. Missouri J. Math. Sci. 27 (2015), no. 1, 47--63. https://projecteuclid.org/euclid.mjms/1449161367

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