@article{MZ_1992__210_1_174393,
     author = {Gabriele Bianchi and Henrik Egnell},
     title = {An {ODE} approach to the equation ... {U} + {Ku} ... = 0, in {Rn.}},
     journal = {Mathematische Zeitschrift},
     pages = {137--166},
     year = {1992},
     volume = {210},
     number = {1},
     zbl = {0759.35019},
     url = {http://geodesic.mathdoc.fr/item/MZ_1992__210_1_174393/}
}