Columbia subject headings:
Keller, Gottfried, 1819-1890--Criticism and interpretation.
Letters in literature.
Harvard subject headings:
Keller, Gottfried, 1819-1890--Criticism and interpretation.
Letters in literature.
Princeton subject headings:
Keller, Gottfried, 1819-1890--Correspondence.
Keller, Gottfried, 1819-1890--Criticism and interpretation.