1. D. Chillingworth, “Bifurcation from an orbit of symmetry,” in: Singularities and Dynamical Systems, S. N. Pnevmatikos (Ed.), North-Holland Mathematics Studies, Amsterdam (1985), pp. 285–294.
2. D. Chillingworth, “Generic multiparameter bifurcation from a manifold,” Dynam. Stab. Syst., 15, 101–137 (2000).
3. E. N. Dancer, “Breaking of symmetries for forced equations,” Math. Ann., 262, 472–485 (1983).
4. J. K. Hale, “Bifurcation near families of solutions,” in: Different. Equat. Proc. Uppsala Int. Conf., in: G. Berg, M. Essen, and A. Pleijl (editors), Acta University of Upsaliensis, Stockholm (1977), pp. 91–100.
5. J. K. Hale and P. Táboas, “Interaction of damping and forcing in a second order equation,” Nonlin. Anal., Theory, Methods Appl., 2, 77–84 (1978).