We study the possibility of extending any bounded Baire-one function on the set of extreme points of a compact convex set to an affine Baire-one function and related questions. We give complete solutions to these questions within a class of Choquet simplices introduced by P. J. Stacey (1979). In particular we get an example of a Choquet simplex such that its set of extreme points is not Borel but any bounded Baire-one function on the set of extreme points can be extended to an affine Baire-one function. We also study the analogous questions for functions of higher Baire classes.
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Let us call a Banach space Plichko (1-Plichko) if it admits a countably norming (countably 1-norming) Markushevich basis. We introduce a subclass of Plichko spaces strictly containing weakly Lindeloef determined spaces which is stable to isomorphisms, subspaces and quotients. Further we prove that each quotient of the space C(0, [omega]1) is 1-Plichko.
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