ABELL, G. O. (1980). Realm of the universe.-- Ed.2. Saunders College.
Lua i Stíl Chicago (17ú heag.)ABELL, George O. Realm of the Universe.-- Ed.2. Philadelphia: Saunders College, 1980.
Lua MLA (9ú heag.)ABELL, George O. Realm of the Universe.-- Ed.2. Saunders College, 1980.
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