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The first conjugate point of solution of the N-th order iterated differential equation. Acta Univ. Palackianae Olomucensis F. R. N., 1982, Тom 73.
Zbl 0522.34029
[2] Borůvka O.:
Lineare Differentialtransformationen 2. Ordnung. VEB Deutscher Verlag der Wissenschaften, Berlin, 1967.
MR 0236448
[3] Vlček V.:
Conjugate points of solutions of an iterated differential equation of the N-th order. Acta Univ. Palackianae Olоmucensis F. R. N., 1983, Тоm 76.
Zbl 0545.34025