[1] Boгůvka O.: Linear Differential Transformations of the Second Order. Thе Engliѕh Univегѕitiеѕ Prеѕѕ, London, 1971. MR 0463539

[2] Бopyвкa O.: Teopuя глoбaльныx cвoйcmв oбыкнoвeнныx лuнeйныx дuффepeнцuaлъныx ypaвнeнuй вmopoгo nopядкa. Диффеpенциaльные ypaвнения, K28, XII, 1976, 1347-1383.

[3] Borůvka O.: Lectures in the seminar of the Institute of Mathematics of the Czechoslovak Academy of Science in Brno.

[4] Borůvka O.: Sur les blocs des équations différentielles y" = q(t)y aux coefficients périodiques. Rend. Mat. (2), 8, S. VI, 1975, 519-532. MR 0379945

[5] Borůvka O.: Sur quelques compléments á la théorie de Floquet pour les équations différentielles du deuxième ordre. Ann. mat. p. ed appl., S. IV, CH, 1975, 71-77. MR 0374532 | Zbl 0311.34012

[6] Neuman F.: Note on bounded non-periodic solutions of the second-order linear differential equations with periodic coefficients. Mat. Nachrichten, 39, 1969, 217-222. MR 0247193

[7] Neuman F.: Linear differential equations of the second order and their applications. Rend. Math. (3), Vol. 4, Série VI, 1971, 559-617. MR 0311972 | Zbl 0227.34005