In [19], the impossibility of obtaining a positive lower bound of the distances between adjacent zeros of all
solutions of (1) is proved using an example of an equation which has a solution that sticks together with the zero solution
on some interval. In fact, one can show easily that the initial function associated with such solution must coincide with zero
on a proper subinterval of [t0 − τ , t0] (t0 = 0 in [19]) when (2) is satisfied. In addition to this fact, from Lemma 2.1, we
conclude easily that any oscillatory solution from C∗ satisfies that d(x) > τ when (2) holds. These results motivate us to
think that it is possible to find a lower bound of the distance between adjacent zeros of all solutions of (1) with suitable
initial functions when (2) holds. A possible class of initial functions could be the continuous functions with finite number of
zeros on [t0 −τ , t0]. This is connected, also, with Lemma 2.3. Strictly speaking, if Lemma 2.3 holds when x(t) = 0 for some
t ∈ (t1 −τ , t1), then (3) could be used to find a lower bound of the distance between adjacent zeros, which is the same rule
played by Lyapunov’s theorem (see [20, Corollary 5.2]) for second order ordinary differential equations.