1. Birkhoff, G. D.: On the solutions of ordinary linear homogeneous differential equations of the third order, Annals of Math. 12 (1910/11), 103–124.
2. Borůvka, O.: Linear Differentialtransformationen 2. Ordnung, VEB, Berlin 1967; Linear Differential Transformations of the Second Order, The English Univ. Press, London 1971.
3. Borůvka, O.: Teorija global'nych svojstv obyknovennych linejnych differencial'nych uravněnij vtorogo porjadka, Differencial'nyje uravněnija 12 (1976), 1347–1383.
4. Borůvka, O.: Algebraic methods in the theory of global properties of the oscillatory equations Y″ = Q(t)Y. Equadiff IV-Proceedings, Prague 1977, Lecture Notes in Mathematics 703, 35–45.
5. Borůvka, O.: Sur une classe des groupes continus à un paramètre formés des fonctions réelles d'une variable, Ann. Polon. Math., to appear.