[1] Arscott F. M.: Periodic Differential Equations. Pergamon Press, Oxford, 1964. Zbl 0121.29903

[2] Arscott F. M., Sleeman B. D.: Multiplicative Solutions of Linear Differential Equations. J. Lond. Math. Soc, 43 (1968), 263-270. MR 0224911 | Zbl 0155.12503

[3] Erdélyi A.: Asymptotic Expansions. Dover, 1956. MR 0078494

[4] Hermite Ch.: Sur Quelques Applications des Functions Elliptiques. Oeuvres, Vol. III, 264-428.