Hopf, E.
1942
Abzweigung einer periodixhen LoUsung von einer stationaUren LoUsung eines differential-systems.
Ber. Math.-Phys. Kl. SaUchs Acad. Wiss. Leipzig
94,
3–
22. (Transl. in Mabsden, J. E. & McCracken, M. 1976
The Hopf Bifurcation Theorem and its Applications. Springer.)
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