1. Ince, E.L., Ordinary Differential Equations, London, 1926. Translated under the title Obyknovennye differentsial’nye uravneniya, Kharkov, 1939.
2. Ablowitz, M.J. and Clarkson, P.A., Solitons, Nonlinear Evolution Equations and Inverse Scattering, Lect. Notes in Math., Cambridge, 1991, vol. 149.
3. Gromak, V.I. and Lukashevich, N.A., Analiticheskie svoistva reshenii uravnenii Penleve (Analytic Properties of Solutions of Painlevé Equations), Minsk: Universitetskoe, 1990.
4. Aspects of Mathematics;K. Iwasaki,1991
5. Hinkkanen, A. and Laine, I., J. Anal. Math., 1999, vol. 79, pp. 345–377.