[1] Borůvka O.: Lineare Differentialtransformationen 2. Ordnung. DVW, Berlin, 1967.
[2] Rachůnková I.: 
On the theory of phases of academician O. Borůvka. Acta UPO, T. 45 (1974), 63-75. 
MR 0379953 | 
Zbl 0319.34012[3] Rachůnková I.: 
On algebraic properties of dispersions of the 3rd and 4th kind of the differential equation y" = q(t) y. Časopis pro pěst. mat., 100 (1975), 15-26. 
MR 0425268