## Oscillation of second order linear delay differential equations.(English)Zbl 1057.34077

This paper deals with the existence of oscillatory solutions of the equation $u''(t)+ p(t)u(\tau(t))= 0,$ where $$p:\mathbb{R}_+\to \mathbb{R}_+$$ is locally integrable, $$\tau:\mathbb{R}_+\to \mathbb{R}$$ is continuous, $$\tau(t)\leq t$$ for $$t\geq 0$$, $$\tau(t)\to+\infty$$ and $\text{mes}\{s\geq t\mid p(s)> 0\}> 0\quad\text{for }t\geq 0.$ Here, mes denotes the Lebesgue measure on the real line. A number of known results is improved.

### MSC:

 34K11 Oscillation theory of functional-differential equations