  We study distribution functions $F$ that have the property of rational
infinite divisibility: there exist some infinitely divisible distribution
functions $F_1$ and $F_2$ such that $F_1=F*F_2$. We study a class
$\boldsymbol{Q}$ of such distribution functions, which is a wide natural
extension of the well-known class of infinitely divisible distribution
functions. We are interested in general criteria of membership of
$\boldsymbol{Q}$. The obtained conditions are formulated in terms of
characteristic functions and they seem to be convenient for the application.
