Etgen, Garret J.; Lewis, Roger T. A Hille-Wintner comparison theorem for second order differential systems. (English) Zbl 0429.34033 Czech. Math. J. 30(105), 98-107 (1980). MSC: 34C10 PDFBibTeX XMLCite \textit{G. J. Etgen} and \textit{R. T. Lewis}, Czech. Math. J. 30(105), 98--107 (1980; Zbl 0429.34033) Full Text: EuDML
Etgen, Garret J.; Lewis, Roger T. Positive functionals and oscillation criteria for second order differential systems. (English) Zbl 0429.34032 Proc. Edinb. Math. Soc., II. Ser. 22, 277-290 (1979). MSC: 34C10 34A30 34A34 34A40 34C15 PDFBibTeX XMLCite \textit{G. J. Etgen} and \textit{R. T. Lewis}, Proc. Edinb. Math. Soc., II. Ser. 22, 277--290 (1979; Zbl 0429.34032) Full Text: DOI