Bedingungen der Nicht-Oszillationsfähigkeit und der Oszillationsfähigkeit für die lineare Differentialgleichung dritter Ordnung Milan Gera (1971) Matematický časopis
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Boundedness and oscillatoriness of solutions of a nonlinear differential equation of the second order Štefan Kulcsár, Pavol Šoltés (1983) Archivum Mathematicum
Branching of periodic orbits from Kukles isochrones. Toni, B. (1998) Electronic Journal of Differential Equations (EJDE) [electronic only]