ISSN : 1226-0657
Consider a solution y(t) of the nonlinear equation (E) y" + f(t, y) = 0. A solution y(t) is said to be oscillatory if for every T > 0 there exists <TEX>$t_{0}$</TEX> > T such that y(<TEX>$t_{0}$</TEX>) = 0. Let F be the class of solutions of (E) which are indefinitely continuable to the right, i.e. y <TEX>$\in$</TEX> F implies y(t) exists as a solution to (E) on some interval of the form [t<TEX>$\sub$</TEX>y/, <TEX>$\infty$</TEX>). Equation (E) is said to be oscillatory if each solution from F is oscillatory.(omitted)