no. 4
A general-weighted Sturm-Liouville problem
Annali della Scuola Normale Superiore di Pisa - Classe di Scienze, Série 4, Tome 24 (1997) no. 4, pp. 767-782. 
@article{ASNSP_1997_4_24_4_767_0,
     author = {Constantin, Adrian},
     title = {A general-weighted Sturm-Liouville problem},
     journal = {Annali della Scuola Normale Superiore di Pisa - Classe di Scienze},
     pages = {767--782},
     publisher = {Scuola normale superiore},
     volume = {Ser. 4, 24},
     number = {4},
     year = {1997},
     zbl = {0913.34022},
     mrnumber = {1627318},
     language = {en},
     url = {archive.numdam.org/item/ASNSP_1997_4_24_4_767_0/}
}
Constantin, Adrian. A general-weighted Sturm-Liouville problem. Annali della Scuola Normale Superiore di Pisa - Classe di Scienze, Série 4, Tome 24 (1997) no. 4, pp. 767-782. http://archive.numdam.org/item/ASNSP_1997_4_24_4_767_0/

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