Nemesis is a science fiction novel by American writer Isaac Asimov. One of his later science fiction novels, it was published in 1989, three years before his death. The novel is loosely related to the future history of his Robot Series, Empire Series, and Foundation Series, into which Asimov attempted to integrate his science fiction output. This novel is connected to Asimov's other works by several ideas from earlier and later novels, including non-human intelligence, sentient astronomical bodies ("Hallucination"), and rotor engines.

The End of Eternity is a 1955 science fiction novel by Isaac Asimov with mystery and thriller elements on the subjects of time travel and social engineering. Its ultimate premise is that of a causal loop, a type of temporal paradox in which events and their causes form a loop.