1. See e. g. J. Mawhin (2001), 99–115 and the references therein.
2. See e. g. J. Mawhin (1989), 385–396 and the references therein.
3. See e. g. J. Mawhin (2003), 196–215 and the references therein.
4. C. Jordan, Cours d’analyse, vol. 1, Paris, Gauthier-Villars, 1882.
5. T. Flett (1974), 69–70, 72; T. Flett (1980), 62–63.