Columbia subject headings:
Schröder, Rudolf Alexander, 1878-1962--Correspondence.
Zinn, Ernst, 1910-1990--Correspondence.
Harvard subject headings:
Authors, German--20th century--Correspondence
Schröder, Rudolf Alexander, 1878-1962--Correspondence.
Zinn, Ernst, 1910-1990--Correspondence.
Princeton subject headings:
Personal correspondence.
Schröder, Rudolf Alexander, 1878-1962--Correspondence.
Zinn, Ernst, 1910-1990--Correspondence.