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@article{MOMA_1963__67_177200, author = {P. Waltman}, title = {Some {Properties} of {Solutions} of u'' + a(t) f(u) = 0.}, journal = {Monatshefte f\"ur Mathematik}, pages = {50--54}, publisher = {mathdoc}, volume = {67}, year = {1963}, zbl = {0116.29401}, url = {http://geodesic.mathdoc.fr/item/MOMA_1963__67_177200/} }
P. Waltman. Some Properties of Solutions of u'' + a(t) f(u) = 0.. Monatshefte für Mathematik, Tome 67 (1963), pp. 50-54. http://geodesic.mathdoc.fr/item/MOMA_1963__67_177200/