We study the dependence of the Banach-Mazur distance between two subspaces of vector-valued continuous functions on the scattered structure of their boundaries. In the spirit of a result of Y. Gordon (1970), we show that the constant 2 appearing in the Amir-Cambern theorem may be replaced by 3 for some class of subspaces. We achieve this by showing that the Banach-Mazur distance of two function spaces is at least 3, if the height of the set of weak peak points of one of the spaces differs from the height of a closed boundary of the second space. Next we show that this estimate can be improved if the considered heights are finite and significantly different. As a corollary, we obtain new results even for the case of spaces.
机构:
Charles Univ Prague, Fac Math & Phys, Dept Math Anal, Sokolovska 49-83, Prague 8, Czech RepublicCharles Univ Prague, Fac Math & Phys, Dept Math Anal, Sokolovska 49-83, Prague 8, Czech Republic
机构:
Jagiellonian Univ Cracow, Fac Math & Comp Sci, Lojasiewicza 6, PL-30348 Krakow, PolandJagiellonian Univ Cracow, Fac Math & Comp Sci, Lojasiewicza 6, PL-30348 Krakow, Poland
Kobos, Tomasz
Varivoda, Marin
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机构:
Univ Zagreb, Fac Sci, Dept Math, Bijenicka Cesta 30, Zagreb 10000, CroatiaJagiellonian Univ Cracow, Fac Math & Comp Sci, Lojasiewicza 6, PL-30348 Krakow, Poland