1. Duke, W.: When is the product of two Hecke eigenforms an eigenform. In: Number theory in progress, Zakopane-Kościelisko, 1997, vol. 2, pp. 737–741. de Gruyter, Berlin (1999)
2. Emmons, B.A., Lanphier, D.: Products of an arbitrary number of Hecke eigenforms. Acta Arith. 130(4), 311–319 (2007)
3. Ghate, E.: On monomial relations between Eisenstein series. J. Ramanujan Math. Soc. 15(2), 71–79 (2000)
4. Grundlehren der Mathematischen Wissenschaften [Fundamental Principles of Mathematical Sciences];S. Lang,1995
5. Lanphier, D.: Combinatorics of Maass–Shimura operators. J. Number Theory 128(8), 2467–2487 (2008)