1. See F. Klein,Elementarmath. v. höheren Standpunkte aus, T. I, Leipzig, 1908, pp. 296, 352. Consult also E. T. Whittaker,Modern Analysis, Cambridge, 1902, p. 338.
2. A. Cauchy,Cours d'analyse, Paris, 1821, Chap. VII, § I. 1
3. Warren,Phil. Trans., London, 1829, Vol. 119, p. 339.
4. A. Cayley,Coll. Math. Papers, Vol. I, Cambridge, 1889, p. 309.