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Unconditional Orthonormal Systems
Author(s) -
Defant Martin,
Junge Marius
Publication year - 1992
Publication title -
mathematische nachrichten
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.913
H-Index - 50
eISSN - 1522-2616
pISSN - 0025-584X
DOI - 10.1002/mana.19921580117
Subject(s) - mathematics , orthonormal basis , hilbert space , banach space , pure mathematics , constant (computer programming) , trigonometry , space (punctuation) , mathematical analysis , physics , quantum mechanics , computer science , programming language , linguistics , philosophy
We show that a Banach space X is isomorphic to a Hilbert space if and only if the trigonometric system is unconditional in L 2 ( II, X ). If the unconditionally constant is equal to one then X is even isometric to a Hilbert space.