[1] Borůvka O.: Linear Differential Transformations of the Second Order. The English Universities Press, London 1971. MR 0463539

[2] Borůvka O.: On central dispersions of the differential equation y" = q(t)y with periodic coefficients. Lecture Notes in Mаthemаtics, 415, Proceedings of the Conference held аt Dundee, Scotlаnd, 26-29, Mаrch, 1974, 47-60. MR 0450691

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

[4] Bоrůvkа O.: Sur quelques compléments á la théorie de Ғloquet pour les équations différentielles du deuxième ordre. Ann. mаt. p. ed аppl. Ѕ. IV, CII, 1975, 71-77.

[5] Боpувка O.: Teopuя глoбaльныx cвoйcmв oбыкнoвeнныx лuнeйныx дuффepeнцuaльныx ypaвнeнuй вmopoгo нopядкa. Диффepeнциальныe уpавнeния, Hо 8, т. ХII, 1976, 1347-1383.

[6] Лайтоx M.: Pacшupeнue мemoдa Флoкe для onpeдeлeнuя вuдa фyндaмeнmaльнoй cucmeмы peшeнuй дuффepeнцuaлънoгo ypaвнeнuя вmopoгo nopядкa y" = q(t)y. Чex. мат. жуpнал, T. 5 (80), 1955, 164-173.

[7] Mаgnuѕ W. аnd Winkler Ѕ.: Hill's Equation. Interѕсienсe Publiѕherѕ New Yоrk, 1966.

[8] Neumаn F.: Note on bounded non-periodic solutions of second-order linear differential equations with periodic coefficients. Mаth. Nасhr. 39, 1969, 217-222. MR 0247193