Fredrickson, B. (2009). Positivity. Oneworld Publications.
Lua i Stíl Chicago (17ú heag.)Fredrickson, Barbara. Positivity. London: Oneworld Publications, 2009.
Lua MLA (9ú heag.)Fredrickson, Barbara. Positivity. Oneworld Publications, 2009.
Rabhadh: Seans nach mbeach na luanna seo go hiomlán cruinn i ngach uile chás.