was a leader in bringing science fiction out of the low-paying and less prestigious "pulp ghetto". Most of his works, including short stories, have been continuously in print in many languages since their initial appearance and are still available as new paperbacks decades after his death. He was at the top of his form during, and himself helped to initiate, the trend toward social science fiction, which went along with a general maturing of the genre away from space opera to a more literary approach touching on such adult issues as politics and human sexuality. In reaction to this trend, hard science fiction began to be distinguished as a separate subgenre, but paradoxically Heinlein is also considered a seminal figure in hard science fiction, due to his extensive knowledge of engineering and the careful scientific research demonstrated in his stories. Heinlein himself stated—with obvious pride—that in the days before pocket calculators, he and his wife Virginia once worked for several days on a mathematical equation describing an Earth–Mars rocket orbit, which was then subsumed in a single sentence of the novel Space Cadet. Writing style Heinlein is often credited with bringing serious writing techniques to the genre of science fiction. For example, when writing about fictional worlds, previous authors were often limited by the reader's existing knowledge of a typical "space opera" setting, leading to a relatively low creativity level: The same starships, death rays, and horrifying rubbery aliens becoming ubiquitous. This was necessary unless the author was willing to go into long expositions about the setting of the story, at a time when the word count was at a premium in SF. But Heinlein utilized a technique called "indirect exposition", perhaps first introduced by Rudyard Kipling in his own science fiction venture, the Aerial Board of Control stories. Kipling had picked this up during his time in India, using it to avoid bogging down his stories set in India with explanations for his English readers. This technique—mentioning details in a way that lets the reader infer more about the universe than is actually spelled out became a trademark rhetorical technique of both Heinlein and generation of writers influenced by him. Heinlein was significantly influenced by Kipling beyond this, for example quoting him in "On the Writing of Speculative Fiction". Likewise, Heinlein's name is often associated with the competent hero, a character archetype who, though he or she may have