Lapp, R. E. (1981). Matter (2d ed.). Time-Life Books.
Lua i Stíl Chicago (17ú heag.)Lapp, Ralph Eugene. Matter. 2d ed. Hongkong: Time-Life Books, 1981.
Lua MLA (9ú heag.)Lapp, Ralph Eugene. Matter. 2d ed. Time-Life Books, 1981.
Rabhadh: Seans nach mbeach na luanna seo go hiomlán cruinn i ngach uile chás.