Friedrich, S., & Friedel, H. (1989). Stephan Huber: Karl Bornstein Gallery, Santa Monica, july - august 1989 : Galerie Six Friedrich, München, december 89 - january 90 / Redaktion: Six Friedrich. Text: Helmut Friedel. Karl Bornstein Gallery.
توثيق أسلوب شيكاغو (الطبعة السابعة عشر)Friedrich, Six, و Helmut Friedel. Stephan Huber: Karl Bornstein Gallery, Santa Monica, July - August 1989 : Galerie Six Friedrich, München, December 89 - January 90 / Redaktion: Six Friedrich. Text: Helmut Friedel. Santa Monica ; Los Angeles: Karl Bornstein Gallery, 1989.
توثيق جمعية اللغة المعاصرة MLA (الطبعة الثامنة)Friedrich, Six, و Helmut Friedel. Stephan Huber: Karl Bornstein Gallery, Santa Monica, July - August 1989 : Galerie Six Friedrich, München, December 89 - January 90 / Redaktion: Six Friedrich. Text: Helmut Friedel. Karl Bornstein Gallery, 1989.