Characterizations of Faces of Convex Sets in Infinite-dimensional Vector Spaces
摘要
In the paper three different characterizations of faces of convex sets belonging to infinite-dimensional real vector spaces are presented. The first one is formulated in terms of generalized semispaces, the second — in terms of compatible total preorders, and the third — in terms of step-affine functions. All three characterizations are equivalent to each other and extend to infinite-dimensional vector spaces the lexicographical characterization of faces established in finite-dimensional settings by Martinez-Legaz J.-E. (Acta Mathematica Vietnamica. 1997. Vol. 22, No. 1, P. 207–211).