Gaya APA

LOPKER, J., Easton, T, A. (2000). Pictures of personality : guide to the four human natures / John Lopker . Los Angeles: Typology.

Gaya MLA

LOPKER, John., Easton, Thomas, A.. "Pictures of personality : guide to the four human natures / John Lopker". Los Angeles: Typology, 2000. Text.