Ziefle, H. Historical forces, German departments, and the curriculum in small liberal arts colleges in the Midwest: Helmut Ziefle. Teaching German in twentieth century America.(2001).
توثيق أسلوب شيكاغو (الطبعة السابعة عشر)Ziefle, Helmut. "Historical Forces, German Departments, and the Curriculum in Small Liberal Arts Colleges in the Midwest: Helmut Ziefle." Teaching German in Twentieth Century America.(2001) .
توثيق جمعية اللغة المعاصرة MLA (الطبعة الثامنة)Ziefle, Helmut. "Historical Forces, German Departments, and the Curriculum in Small Liberal Arts Colleges in the Midwest: Helmut Ziefle." Teaching German in Twentieth Century America.(2001), .
تحذير: قد لا تكون هذه الاستشهادات دائما دقيقة بنسبة 100%.