Scheel, R. L. (1987). Introduction to the future. ETC Publications.
Lua i Stíl Chicago (17ú heag.)Scheel, Randall L. Introduction to the Future. Palm Springs, Calif.: ETC Publications, 1987.
Lua MLA (9ú heag.)Scheel, Randall L. Introduction to the Future. ETC Publications, 1987.
Rabhadh: Seans nach mbeach na luanna seo go hiomlán cruinn i ngach uile chás.