Ogni spazio di Banach ha un sistema bibasico normalizzato; inoltre ogni successione uniformemente minimale appartiene ad un sistema biortogonale limitato , dove è M-basica e normante.
@article{RLINA_1984_8_77_1-2_28_0, author = {Anatoli Pli\v cko and Paolo Terenzi}, title = {On bibasic systems and a Retherford's problem}, journal = {Atti della Accademia Nazionale dei Lincei. Classe di Scienze Fisiche, Matematiche e Naturali. Rendiconti}, volume = {76}, year = {1984}, pages = {28-34}, zbl = {0609.46008}, mrnumber = {0884374}, language = {en}, url = {http://dml.mathdoc.fr/item/RLINA_1984_8_77_1-2_28_0} }
Pličko, Anatoli; Terenzi, Paolo. On bibasic systems and a Retherford’s problem. Atti della Accademia Nazionale dei Lincei. Classe di Scienze Fisiche, Matematiche e Naturali. Rendiconti, Tome 76 (1984) pp. 28-34. http://gdmltest.u-ga.fr/item/RLINA_1984_8_77_1-2_28_0/
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