1. J M Abdulrahman, Bifurcation of limit cycles of some polynomial systems (PhD thesis, The University College of Wales, Aberystwyth, 1989).
2. T R Blows and N G Lloyd, ‘The number of limit cycles of certain polynomial differential equations’, Proc. Roy. Soc. Edinburgh Sect. A 98 (1984) 215–239.
3. C J Christopher and N G Lloyd, ‘On the paper of Jin and Wang concerning the conditions for a centre in certain cubic systems’, Bull. London Math. Soc., 94 (1990) 5–12.
4. C J Christopher and N G Lloyd, ‘Invariant algebraic curves and conditions for a centre’, pre print, The University College of Wales, Aberystwyth, 1989.
5. E M James and N G Lloyd, ‘A cubic system with eight small-amplitude limit cycles’, preprint The University College of Wales, Aberystwyth, 1990.