Lopker, J. (2000). Pictures of personality: Guide to the four human natures (First edition.). Typology.
Lua i Stíl Chicago (17ú heag.)Lopker, John. Pictures of Personality: Guide to the Four Human Natures. First edition. Los Angeles, CA: Typology, 2000.
Lua MLA (8ú heag.)Lopker, John. Pictures of Personality: Guide to the Four Human Natures. First edition. Typology, 2000.
Rabhadh: Seans nach mbeach na luanna seo go hiomlán cruinn i ngach uile chás.