[1] F. M. Arscott: Studies in multiplicative solutions of linear differential equations. Proc. Roy. Soc., Edinburgh, 106A, (1987), 277-305. MR 0906213

[2] F. M. Arscott, B. D. Sleeman: Multiplicative solutions of linear differential equations. J. Lond. Math. Soc. (2), 43 (1968), 263-270. MR 0224911 | Zbl 0155.12503

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

[4] Erdélyi, al. : Higher Transcendental Functions. (Bateman Manuscript Project) Vol. III, McGraw-Hill, 1955.

[5] E. L. Ince: Ordinary Differential Equations. Longmans - Dover, 1927. MR 0010757