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.

vichy is a "commune" in central france, in the auvergne-rhône-alpes region, along the allier river.
vichy

the calculus of variations is a field of mathematical analysis.
calculus of variations

yosef hamadani cohen (; born 1916 – 29 march 2014) was an iranian jewish religious leader.

yosef hamadani cohen