@article{RSMUP_1956__25__214_0,
     author = {Hille, Einar},
     title = {On a class of orthonormal functions},
     journal = {Rendiconti del Seminario Matematico della Universit\`a di Padova},
     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/}
}