1. An Introduction to Gröbner Bases
2. N. N. Bautin, On the number of limit cycles which appear with the variation of coefficients from an equilibrium position of focus or center type, Math. Sbornik N. S. 30(1952) 181--196; Translation Amer. Math. Soc. 100(1954) 181--196.
3. Local Theory of Nonlinear Analytic Ordinary Differential Equations
4. A survey of isochronous centers
5. Linearizability and local bifurcation of critical periods in a cubic Kolmogorov system