Eliseenko, M. N. On periodic solutions of second order ordinary differential equations not in explicit form with respect to the derivative. (Russian) Zbl 0604.34023 Differ. Uravn. 21, No. 9, 1618-1621 (1985). Reviewer: G.Bojadziev MSC: 34C25 PDFBibTeX XMLCite \textit{M. N. Eliseenko}, Differ. Uravn. 21, No. 9, 1618--1621 (1985; Zbl 0604.34023)
Myshkis, A. D. On Sturm type theorems for linear systems of differential equations. (Russian) Zbl 0594.34010 Differ. Uravn. 21, No. 9, 1639-1641 (1985). Reviewer: E.Barvinek MSC: 34A30 PDFBibTeX XMLCite \textit{A. D. Myshkis}, Differ. Uravn. 21, No. 9, 1639--1641 (1985; Zbl 0594.34010)