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The only two complete books ( as opposed to essays ) published in his lifetime , " Walden " and " A Week on the Concord and Merrimack Rivers " ( 1849 ) , both dealt with nature , in which he " loved to wander " .
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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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