Bifurcation of critical periods from Pleshkan's isochrones
Bifurcation of critical periods from Pleshkan's isochrones
Pleshkan proved in 1969 that, up to a linear transformation and a constant rescaling of time, there are four isochrones in the family of cubic centers with homogeneous nonlinearities $\mathscr C_3.$ In this paper we prove that if we perturb any of these isochrones inside $\mathscr C_3,$ then at most …