@article{700208,
     title = {On ordinary linear differential equations of high order},
     booktitle = {Differential Equations and Their Applications},
     series = {GDML\_Books},
     publisher = {Slovensk\'e pedagogick\'e nakladate\v lstvo},
     address = {Bratislava},
     year = {1967},
     pages = {193-199},
     zbl = {0187.33702},
     url = {http://dml.mathdoc.fr/item/700208}
}

Hornich, H. On ordinary linear differential equations of high order, dans Differential Equations and Their Applications, GDML_Books,  (1967), pp. 193-199. http://gdmltest.u-ga.fr/item/700208/