@article{ASNSP_2010_5_9_3_635_0,
     author = {Bony, Jean-Michel and Colombini, Ferruccio and Pernazza, Ludovico},
     title = {On square roots of class $C^m$ of nonnegative functions of one variable},
     journal = {Annali della Scuola Normale Superiore di Pisa - Classe di Scienze},
     pages = {635--644},
     publisher = {Scuola Normale Superiore, Pisa},
     volume = {Ser. 5, 9},
     number = {3},
     year = {2010},
     mrnumber = {2722658},
     zbl = {1207.26004},
     language = {en},
     url = {http://archive.numdam.org/item/ASNSP_2010_5_9_3_635_0/}
}