10 Algebraic structure of the set of phases of oscillatory differential equations (q) in the interval (-∞, ∞)
(English).
In:
Borůvka, Otakar; Arscott, F. M. (translator): Linear Differential Transformations of the Second Order.
(English).
London:
The English Universities Press, Ltd.,
1971.
0-340-12408-3,
pp. [102]-105
