@article{ASNSP_1966_3_20_3_543_0,
     author = {Berger, Melvyn S.},
     title = {A {Sturm-Liouville} theorem for nonlinear elliptic partial differential equations},
     journal = {Annali della Scuola Normale Superiore di Pisa - Scienze Fisiche e Matematiche},
     pages = {543--582},
     publisher = {Scuola normale superiore},
     volume = {Ser. 3, 20},
     number = {3},
     year = {1966},
     mrnumber = {211299},
     zbl = {0147.09503},
     language = {en},
     url = {http://www.numdam.org/item/ASNSP_1966_3_20_3_543_0/}
}