1. L. Biberbach, Analytic Continuation [in Russian], Nauka, Moscow (1967).
2. R. P. Stanley, Enumerative Combinatorics, Cambridge Univ. Press, Cambridge (2012).
3. A. G. Rutkas, “Spectral methods for studying degenerate differential-operator equations. I” [in Russian], Sovrem. Mat. Pril. 35 (2005); English transl.: J. Math. Sci., New York 144, No. 4, 4246–4262 (2007).
4. A. Favini and A. Yagi, Degenerate Differential Equations in Banach Spaces, Marcel Dekker, New York etc. (1999).
5. S. L. Gefter and T. E. Stulova, “Fundamental solution of the simplest implicit linear differential equation in a vector space” [in Russian], Probl. Mat. Anal. 78, 47–55 (2015); English transl.: J. Math. Sci., New York 207, No. 2, 166–175 (2015).