@inbook{401677,
     title = {8 Elementary phases},
     booktitle = {Linear Differential Transformations of the Second Order},
     series = {GDML\_Books},
     publisher = {The English Universities Press, Ltd.},
     address = {London},
     year = {1971},
     pages = {[87]-93},
     url = {http://dml.mathdoc.fr/item/401677}
}