10 Algebraic structure of the set of phases of oscillatory differential equations (q) in the interval (-∞, ∞)
Linear Differential Transformations of the Second Order, GDML_Books, (1971), p. [102]-105 / Harvested from
Access to full text
Full (PDF) 
@inbook{401679,
     title = {10 Algebraic structure of the set of phases of oscillatory differential equations (q) in the interval (-$\infty$, $\infty$)},
     booktitle = {Linear Differential Transformations of the Second Order},
     series = {GDML\_Books},
     publisher = {The English Universities Press, Ltd.},
     address = {London},
     year = {1971},
     pages = {[102]-105},
     url = {http://dml.mathdoc.fr/item/401679}
}

 (éd.). 10 Algebraic structure of the set of phases of oscillatory differential equations (q) in the interval (-∞, ∞), dans Linear Differential Transformations of the Second Order, GDML_Books,  (1971), pp. [102]-105. http://gdmltest.u-ga.fr/item/401679/