A Dirichlet Series Associated to Eisenstein Series of Degree Two. Erik Lippa — 1974 Mathematische Zeitschrift
Correction and Supplement: An Elementary Approach to Hecke Operators. Erik A. Lippa — 1975 Mathematische Annalen
Hecke Eigenforms of Degree Two: Dirichlet Series and Euler Products. Erik A. Lippa — 1976 Mathematische Annalen