We shall assume that functions p(t) and f (t,y, z) are sufficiently smooth so that Eq. (1.1) always has solutions that
are continuable throughout [t0,∞). Such a solution of Eq. (1.1) is called oscillatory if it has arbitrarily large zeros,
otherwise it is called nonoscillatory. Finally, Eq. (1.1) is called oscillatory if all its solutions are oscillatory