1. Integrability and algebraic solutions for planar polynomial differential systems with emphasis on the quadratic systems;Cairó;Resenhas de Universidade de São Paulo,1999
2. Darboux integrability and invariant algebraic curves for planar polynomial systems;Christopher;J. Phys. A,2002
3. Invariant algebraic curves and conditions for a center;Christopher;Proc. Roy. Soc. Edinburgh Sect. A,1994
4. C. Christopher, Polynomial systems with invariant algebraic curves, preprint, 1993
5. Polynomial vector fields with prescribed algebraic limit cycles;Christopher;Geom. Dedicata,2001