what are its main source of economy?
Real estate.
London
 London has some of the highest real estate prices in the world.
what is future science fiction and science fiction stories? Two American science fiction magazines. who was its editor? Charles Hornig when was it initially published? End of the 1930s. who owns it? Louis Silberkleit can you name any works they published? "The Liberation of Earth",  "If I Forget Thee, Oh Earth" can you summarize the plot of the first work? It portrays Earth as the battleground between two powerful alien races, the Troxxt and the Dendi, who repeatedly "liberate" it from each other. who is the writer? William Tenn when was the work published? 1953 what was its response? Nick Gevers has described "The Liberation of Earth" as "great", and "Locus" columnist Rich Horton described it as "one of 1953's best shorts". what can you tell me about the second one? The themes in the story exploit the anxieties prevalent at the time regarding nuclear warfare. what are the other works of the aforesaid writer? "Child's Play" and  "Alexander the Bait". where was he born? London when did he begin his writing career? May 1946 can you tell me more about his birthplace mentioned above? It is the capital and largest city of England and the United Kingdom.
wiki:7751876
London [SEP] Economy
London's gross regional product in 2018 was almost £500 billion, around a quarter of UK GDP. London has five major business districts: the city, Westminster, Canary Wharf, Camden & Islington and Lambeth & Southwark. One way to get an idea of their relative importance is to look at relative amounts of office space: Greater London had 27 million m of office space in 2001, and the City contains the most space, with 8 million m of office space. London has some of the highest real estate prices in the world. London is the world's most expensive office market for the last three years according to world property journal (2015) report.