Gaya APA
Riso, D, R. (1987).
Personality types: Using the Enneagram for self-discovery. .
Boston:
Boston Houghton Mifflin Company.
Gaya MLA
Riso, Don, Richard.
"Personality types: Using the Enneagram for self-discovery. ".
Boston:
Boston Houghton Mifflin Company,
1987.
Buku.