Generate a topic word for the given sentence. A topic word is usually the name of a person, place, animal, concept or object the sentence is focusing on.
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Question: the calculus of variations is a field of mathematical analysis.

Answer: calculus of variations


Question: "the raven" is a narrative poem by american writer edgar allan poe, first published in january 1845.

Answer: the raven


Question: the title of duke of nemours was originally given to a french family of minor nobility.

Answer:
duke of nemours