On a class of orthonormal functions
Rendiconti del Seminario Matematico della Università di Padova, Tome 25 (1956), pp. 214-249. 
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     author = {Hille, Einar},
     title = {On a class of orthonormal functions},
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     pages = {214--249},
     publisher = {Seminario Matematico of the University of Padua},
     volume = {25},
     year = {1956},
     mrnumber = {86974},
     zbl = {0071.30201},
     language = {en},
     url = {http://www.numdam.org/item/RSMUP_1956__25__214_0/}
}
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Hille, Einar. On a class of orthonormal functions. Rendiconti del Seminario Matematico della Università di Padova, Tome 25 (1956), pp. 214-249. http://www.numdam.org/item/RSMUP_1956__25__214_0/

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