 Examples are Ray Bradbury's "The Martian Chronicles" and Isaac Asimov's "I, Robot", both of which read as a series of short stories which may share plot threads and characters but which still act as self-contained stories.By contrast, van Vogt's "The Weapon Shops of Isher" is structured like a continuous novel although it incorporates material from three previous Van Vogt short stories.Fix-ups became an accepted practice in American publishing during the 1950s, when science fiction and fantasy—once published primarily in magazines—began appearing increasingly in book form.