[1] Sherman T. L.:
Properties of solutions of $N^{\text th}$ order linear differential equations. Pacific J. Math, Vol. 15, No. 3, 1965
MR 0185185
[2] Borůvka O.:
Lineare Differentialtransformationen 2. Ordnung. VEB Deutscher Verlag der Wissenschaften, Berlin, 1967
MR 0236448 |
Zbl 0153.11201
[3] Vlček V.:
On a distribution of zeros of solutions of a fourth-order iterated linear differential equation. Acta UP Olom., F. R. N., Tom 57, 1978
MR 0554040 |
Zbl 0422.34037