Differential equations and dynamical systems. Proceedings of an international symposium held at the University of Puerto Rico, Mayaguez, Puerto Rico, December 27-30, 1965. (Sponsored by the United States Air Force Office of Scientific Research, the University of Puerto Rico, and Brown University) /
United States.Air Force.Air Research and Development Command.Office of Scientific Research.
Hale, Jack K.
LaSalle, Joseph P.
New York & London, 
1967.