and fans active in the field came to associate the term with low-budget, low-tech "B-movies" and with low-quality pulp science fiction. By the 1970s, critics within the field, such as Damon Knight and Terry Carr, were using "sci fi" to distinguish hack-work from serious science fiction. Peter Nicholls writes that "SF" (or "sf") is "the preferred abbreviation within the community of sf writers and readers." Robert Heinlein found even "science fiction" insufficient for certain types of works in this genre, and suggested the term speculative fiction to be used instead for those that are more "serious" or "thoughtful." History Some scholars assert that science fiction had its beginnings in ancient times, when the line between myth and fact was blurred. Written in the 2nd century CE by the satirist Lucian, A True Story contains many themes and tropes characteristic of modern science fiction, including travel to other worlds, extraterrestrial lifeforms, interplanetary warfare, and artificial life. Some consider it the first science-fiction novel. Some of the stories from The Arabian Nights, along with the 10th-century The Tale of the Bamboo Cutter and Ibn al-Nafis's 13th-century Theologus Autodidactus, also contain elements of science fiction. Written during the Scientific Revolution and the Age of Enlightenment, Johannes Kepler's Somnium (1634), Francis Bacon's New Atlantis (1627), Athanasius Kircher's Itinerarium extaticum (1656), Cyrano de Bergerac's Comical History of the States and Empires of the Moon (1657) and The States and Empires of the Sun (1662), Margaret Cavendish's "The Blazing World" (1666), Jonathan Swift's Gulliver's Travels (1726), Ludvig Holberg's Nicolai Klimii Iter Subterraneum (1741) and Voltaire's Micromégas (1752) are sometimes regarded as some of the first true science-fantasy works. Isaac Asimov and Carl Sagan considered Somnium the first science-fiction story; it depicts a journey to the Moon and how the Earth's motion is seen from there. Following the 17th-century development of the novel as a literary form, Mary Shelley's Frankenstein (1818) and The Last Man (1826) helped define the form of the science-fiction novel. Brian Aldiss has argued that Frankenstein was the first work of science fiction. Edgar Allan Poe wrote several stories considered to be science fiction, including "The Unparalleled Adventure of One Hans Pfaall" (1835), which featured a trip to the Moon. Jules Verne was noted for his attention to detail and scientific accuracy, especially in Twenty Thousand Leagues Under the Sea (1870). In 1887, the novel El anacronópete by Spanish author Enrique Gaspar y