Quadratic systems with a degenerate critical point

W. A. Coppel
1988 Bulletin of the Australian Mathematical Society  
It is shown that a quadratic system with a degenerate critical point has at most one limit cycle. Since 7 is stable we must have h < 0. We will assume h -0 and derive a contradiction. https://www.cambridge.org/core/terms. https://doi.
doi:10.1017/s0004972700027167 fatcat:fa757r3wrbgrne2h2dmnkxtam4