The stories were not initially conceived as a set, but rather all feature his positronic robots—indeed, there are some inconsistencies among them, especially between the short stories and the novels.
Pripovijesti izvorno nisu bile pisane kao dio veće cjeline, nego im je zajedničko bilo to da govore o pozitronskim robotima - i zaista, postoje nedosljednosti, osobito između kratkih priča i romana.