Gaya APA

Hudson, D, R, R, &, R. (2000). Understanding the Enneagram: The practikal guide to personality types (Cetakan 1). New York: Houghton Mifflin.

Gaya MLA

Hudson, Don, Richard, Riso, &, Russ. "Understanding the Enneagram: The practikal guide to personality types". Cetakan 1 New York: Houghton Mifflin, 2000. Text.