1. Borwein, J.M., Crandall, R.E.: Closed forms: what they are and why we care. Not. AMS 60, 50–65 (2013)
2. Coddington, E.A.: Theory of Ordinary Differential Equations. McGraw-Hill, New York (1984)
3. Drach, J.: Essai sur une théorie général de l’intégration et sur la classification des transcendentes. Gauthier-Villars, Paris (1898)
4. Drazin, P.G., Riley, N.: The Navier–Stokes Equations: A Classification of Flows and Exact Solutions. Cambridge University Press, Cambridge (2006)
5. Forsyth, A.R.: Lehrbuch der Differentialgleichungen. Vieweg, Braunschweig (1889)