[1] M. Бapтyшек: O нyляx кoлеблющиxcя pешений ypaвнения $(p(x)x')' + f(t, x, x') = 0$. Дифф. ypaв., XII, Но. 24, 621-625.
[2] M. Bartušеk:
On Zeros of Solutions of the Differential Equation $(p(t)y')' + f(t,y,y') = 0$. Arch. Math., XI, No. 4, 187-192.
MR 0409975
[3] M. Bartušek:
Monotonicity Theorems concerning Differential Equations $y" +f(t,y,y') = 0$. Arch. Math., XII, No. 4, 1976, 169-178.
MR 0430410
[4] M. Bartušek:
On Zeros of Solutions of the Differential Equation $y" + f(t,y)g(y') = 0$. Aгch. Math., XV, 3, 129-132.
MR 0562336
[5] I. Bihaгi:
Oscillation and Monotonity Theorems Concerning Non-linear Differential Equations of the Second Order. Acta Math. Acad. Sci. Нung., IX, No. 1-2, 1958, 83-104.
MR 0095321
[6] K. M. Daѕ:
Comparison and Monotonity Theorems for Second Order Non-linear Differential Equations. Acta Math. Sci. Hung., XV, No. 3-4, 1964, 449-456.
MR 0176155
[7] A. Г. Kaтpaмoв: Oб acuмnmomuчecкoм noвeдeнuu кoлeблющuxcя peшeнuй ypaвлeнuя $\ddot{x} + f(t, x)g(\dot{x}) = 0$. Дифф. ypaблeния, VIH, Но. 6, 1972, 1111-1115.