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He was no stranger to television science fiction , having written three serials for " Doctor Who " and having acted as script editor on the entire four season run of " Blake 's 7 " as well as writing nine episodes for it himself .
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Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: location, person, organization 
Text: {0} 
Answer:
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