Universal centers and composition conditions on the complex plane

CLAUDIA VALLS
2021 Carpathian Journal of Mathematics  
We characterize the universal centers of the ordinary differential equations in the complex plane $d \rho/d \theta=\sum_{i=1}^\infty a_i(\theta) \rho^{i+1}$, where $a_i(\theta)$ are trigonometric polynomials with complex coefficients, in terms of the composition conditions.
doi:10.37193/cjm.2021.01.13 fatcat:4mlxlt4oyjfpnef63ztvn7srby