Gaya APA

Riso, D, R. (1987). Personality types: Using the Enneagram for self-discovery. . Boston: Boston Houghton Mifflin Co.

Gaya MLA

Riso, Don, Richard. "Personality types: Using the Enneagram for self-discovery. ". Boston: Boston Houghton Mifflin Co, 1987. Buku.