A Necessary Condition for the Existence of Periodical Solutions of a Differential System

Julka Knežević-Miljanović

The problem of necessary conditions for the existence of
periodical solutions of the system $X'=\f(t)P(X)+Q(t)$ is considered, where
$\f(t)$, $Q_i(t)$ ($i=1,\dots,n$) are continuous functions belonging to
certain classes.