@article{702184,
     title = {On the properties of linear differential equations of the second order in the complex domain},
     booktitle = {Differential Equations and Their Applications},
     series = {GDML\_Books},
     publisher = {Publishing House of the Czechoslovak Academy of Sciences},
     address = {Prague},
     year = {1963},
     pages = {179-186},
     mrnumber = {MR0174816},
     zbl = {0173.10002},
     url = {http://dml.mathdoc.fr/item/702184}
}

Šeda, V. On the properties of linear differential equations of the second order in the complex domain, dans Differential Equations and Their Applications, GDML_Books,  (1963), pp. 179-186. http://gdmltest.u-ga.fr/item/702184/