Unknown. (1931). Letter in German, February 9, 1931. Saint Louis University Libraries Digitization Center.
Citace podle Chicago (17th ed.)Unknown. Letter in German, February 9, 1931. Saint Louis University Libraries Digitization Center, 1931.
Citace podle MLA (8th ed.)Unknown. Letter in German, February 9, 1931. Saint Louis University Libraries Digitization Center, 1931.
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