Srishti D. Chatterji, Cours d'analyse, vol. 2 : Analyse complexe, PPUR, (lire en ligne), p. 96.
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(en) Alan Sultan et Alice F. Artzt, The mathematics that every secondary school math teacher needs to know, Studies in Mathematical Thinking and Learning, Taylor & Francis, 2010, p. 326.
L. Euler, Introduction à l'analyse infinitésimale, article 138.