Heuduck, A. a. W. (1949). Letter to Gerdt Wagner also Letter in German to Paul Heuduck, Janurary 26, 1949 and January 23, 1948. Saint Louis University Libraries Digitization Center.
توثيق أسلوب شيكاغو (الطبعة السابعة عشر)Heuduck, Arno and Wagner. Letter to Gerdt Wagner Also Letter in German to Paul Heuduck, Janurary 26, 1949 and January 23, 1948. Saint Louis University Libraries Digitization Center, 1949.
توثيق جمعية اللغة المعاصرة MLA (الطبعة الثامنة)Heuduck, Arno and Wagner. Letter to Gerdt Wagner Also Letter in German to Paul Heuduck, Janurary 26, 1949 and January 23, 1948. Saint Louis University Libraries Digitization Center, 1949.
تحذير: قد لا تكون هذه الاستشهادات دائما دقيقة بنسبة 100%.