[1] Blaschke W.: Vorlesungen über Differentialgeometrie II. Springer, Berlin 1923.

[2] Borůvka O.: Sur quelques applications des dispersions centrales dans la théorie des equations différentielles linéaires du deuxième ordre. Archivum mathematicum (Brno), T. 1 (1965), 1-20. MR 0197823

[3] Borůvka O.: Lineare Differentialtransformationen 2. Ordnung. VEB Berlin, 1967.

[4] Cesari L.: Asymptotic Behavior and Stability Problems in Ordinary Differential Equations. MIR, Moscow 1964. MR 0180708 | Zbl 0121.07203

[5] Neuman F.: Sur les équations differentielles linéaires oscillatoires du deuxième ordre avec la dispersion fondamentale $\varphi (t) = t + \pi$. Buletinul Inst. Polit. (Iaşi), T. X (XIV), (1964), 37-42. MR 0197825 | Zbl 0151.12202

[6] Neuman F.: Criterion of Periodicity of Solutions of a Certain Differential Equation with a Periodic Coefficient. Ann. di Mat. p. ed appl. (IV), T. LXXV (1967), 385-396. MR 0213652 | Zbl 0148.07104

[7] Neuman F.: Extremal Property of the Equation $y" = -k^2 y$. Archivum math. (Brno), T. 3 (1967), 161-164. MR 0236465

[8] Neuman F.: Relation between the Distribution of the Zeros of the Solutions of a 2nd Order Linear Differential Equation and the Boundedness of these Solutions. Acta Math., T. XIX (1968), p. 1-6. MR 0228750

[9] Santaló L. A.: Introduction to Integral Geometry. Hermann, Paris 1953. MR 0060840