Freeman, R. A. (1936). The Penrose mystery. Blue Ribbon Books.
Lua i Stíl Chicago (17ú heag.)Freeman, R. Austin. The Penrose Mystery. New York: Blue Ribbon Books, 1936.
Lua MLA (8ú heag.)Freeman, R. Austin. The Penrose Mystery. Blue Ribbon Books, 1936.
Rabhadh: Seans nach mbeach na luanna seo go hiomlán cruinn i ngach uile chás.