11. Letter from Leon A. Heppel to Maxine Singer Creator: Cornell UniversityHeppel, Leon A. Date: [3 June 1974] Genre: Letters (correspondence)
12. Letter from Leon A. Heppel to Maxine Singer Creator: Heppel, Leon A. Date: 9 March 1988 Genre: Letters (correspondence)
13. Letter from Leon A. Heppel to Maxine Singer Creator: Heppel, Leon A. Date: 21 March 1977 Genre: Letters (correspondence)
14. Letter from Leon A. Heppel to Maxine Singer Creator: Heppel, Leon A. Date: [14 July 1958] Genre: Letters (correspondence)