##
**On strongly convex sets and strongly convex functions.**
*(English.
Russian original)*
Zbl 0983.52001

J. Math. Sci., New York 100, No. 6, 2633-2681 (2000); translation from Itogi Nauki Tekh., Ser. Sovrem. Mat. Prilozh., Temat. Obz. 61, 66-138 (1999).

The basic notions of this paper are generating set and \(M\)-strongly convex set, which have grown from the axiomatic approach to the notion of convexity. A convex closed set \(M\) of a Banach space \(E\) is called a generating set if for any nonempty set \(A\) of the form \(A=\bigcap_{x\in X}(M+x)\) one can find a convex closed set \(B\subset E\) such that \(\overline{A+B}=M\). For a given generating set \(M\) a nonempty set of the above form is called an \(M\)-strongly convex set. The author obtains necessary and sufficient conditions for a set to be a generating one and presents classes of generating sets, operations with generating sets that preserve the generating property, general properties of \(M\)-strongly convex sets for an arbitrary generating set \(M\) and conditions for preservation of the \(M\)-strong convexity.

There are also introduced and studied the concepts of the \(M\)-strongly convex hull, \(R\)-strongly extreme point and \(R\)-strongly exposed point of a set. One can find here generalizations of the Carathéodory theorem on a representation of convex hull of a set in \(R^n\) and the Krein-Mil’man theorem on extreme points of a compact set in \(R^n\). Moreoever there is presented a new class of Lipschitzian single-valued selectors of convex- and compact-valued multivalued mappings. The author studies the class of generating sets which are the epigraphs of certain convex functions. He defines the concepts of a generating function \(m\), an \(m\)-strongly convex function (generalization of the notion of the strongly convex function) and an epidifference of functions (based on the Minkowski-Pontryagin difference of epigraphs of functions). He obtains a criterion for a function \(m\) to be a generating one and conditions for \(m\)-strong convexity of a given function.

The paper includes a lot of interesting examples.

There are also introduced and studied the concepts of the \(M\)-strongly convex hull, \(R\)-strongly extreme point and \(R\)-strongly exposed point of a set. One can find here generalizations of the Carathéodory theorem on a representation of convex hull of a set in \(R^n\) and the Krein-Mil’man theorem on extreme points of a compact set in \(R^n\). Moreoever there is presented a new class of Lipschitzian single-valued selectors of convex- and compact-valued multivalued mappings. The author studies the class of generating sets which are the epigraphs of certain convex functions. He defines the concepts of a generating function \(m\), an \(m\)-strongly convex function (generalization of the notion of the strongly convex function) and an epidifference of functions (based on the Minkowski-Pontryagin difference of epigraphs of functions). He obtains a criterion for a function \(m\) to be a generating one and conditions for \(m\)-strong convexity of a given function.

The paper includes a lot of interesting examples.

### MSC:

52A01 | Axiomatic and generalized convexity |

52A41 | Convex functions and convex programs in convex geometry |

52A20 | Convex sets in \(n\) dimensions (including convex hypersurfaces) |

49J45 | Methods involving semicontinuity and convergence; relaxation |

26B25 | Convexity of real functions of several variables, generalizations |

58B05 | Homotopy and topological questions for infinite-dimensional manifolds |

54C65 | Selections in general topology |

### Keywords:

generating set; \(M\)-strongly convex set; generating function; \(m\)-strongly convex function; \(M\)-strongly convex hull; \(R\)-strongly extreme point; Minkowski-Pontryagin difference### References:

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