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JOURNALS // Matematicheskii Sbornik // Archive

Mat. Sb., 2025 Volume 216, Number 6, Pages 138–150 (Mi sm10132)

On the density of the additive semigroup generated by a subset of a Hilbert–Schmidt ellipsoid

K. S. Shklyaevab

a Faculty of Mechanics and Mathematics, Lomonosov Moscow State University, Moscow, Russia
b Moscow Center of Fundamental and Applied Mathematics, Moscow, Russia

Abstract: We obtain a criterion for the density of the additive semigroup generated by a subset of an ellipsoid in a Hilbert space with finite sum of the squared semiaxes. This criterion is then applied to the semigroups generated by the images of sets under holomorphic maps. As a consequence, we obtain a result on the uniform approximation of a holomorphic function on compact subsets by sums of shifts of a single function which generalizes Korevaar's theorem.
Bibliography: 7 titles.

Keywords: approximation, additive semigroup, Hilbert space, ellipsoid, shift.

MSC: 30E10, 41A46, 41A65, 43A15

Received: 04.06.2024 and 10.01.2025

DOI: 10.4213/sm10132


 English version:
Sbornik: Mathematics, 2025, 216:6, 864–875

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© Steklov Math. Inst. of RAS, 2026