@article{PORMA_1977__36_3-4_115318,
     author = {Derrick, W.R.},
     title = {Nonlinear functional {Sturm-Liouville} equations},
     journal = {Portugaliae mathematica},
     pages = {227--237},
     publisher = {mathdoc},
     volume = {36},
     number = {3-4},
     year = {1977},
     mrnumber = {0597844},
     zbl = {0451.34018},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/PORMA_1977__36_3-4_115318/}
}