ASTIN, A. W. (1991). Four critical years. Jossey Bass.
Lua i Stíl Chicago (17ú heag.)ASTIN, Alexander W. Four Critical Years. Jossey Bass, 1991.
Lua MLA (8ú heag.)ASTIN, Alexander W. Four Critical Years. Jossey Bass, 1991.
Rabhadh: Seans nach mbeach na luanna seo go hiomlán cruinn i ngach uile chás.