One Upper Estimate on the Number of Limit Cycles of Even Degree Li\'enard Equations in the Focus Case

We give an explicit upper bound for a number of limit cycles of the Li\'enard equation $\dot{x}=y-F(x)$, $\dot{y}=-x$ of even degree in the case its unique singular point $(0,0)$ is a focus.Comment: 10 pages, 1 figur