Schwager, M. (1949). Letter to Paul Heuduck, September 13, 1949. Saint Louis University Libraries Digitization Center.
Chicago-viite (17. p.)Schwager, Mortimer. Letter to Paul Heuduck, September 13, 1949. Saint Louis University Libraries Digitization Center, 1949.
MLA-viite (8. p.)Schwager, Mortimer. Letter to Paul Heuduck, September 13, 1949. Saint Louis University Libraries Digitization Center, 1949.
Varoitus: Nämä viitteet eivät aina ole täysin luotettavia.