Douglas Adams (2012). “The Hitchhiker's Guide to the Galaxy Radio Scripts Volume 2: The Tertiary, Quandary and Quintessential Phases”, p.83, Pan Macmillan
Douglas Adams (2012). “The Hitchhiker's Guide to the Galaxy Radio Scripts Volume 2: The Tertiary, Quandary and Quintessential Phases”, p.42, Pan Macmillan