* {{cite book | last=Berger | first=Harold L. | title=Science Fiction and the New Dark Age | publisher=Bowling Green, Ohio : Bowling Green University Popular Press | publication-place=Bowling Green, Ohio | date=1976 | isbn=0-87972-121-9}}
<ref name="g593">{{cite book | last=Berger | first=Harold L. | title=Science Fiction and the New Dark Age | publisher=Bowling Green, Ohio : Bowling Green University Popular Press | publication-place=Bowling Green, Ohio | date=1976 | isbn=0-87972-121-9 | page=}}</ref>