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.

[Q]: vichy is a "commune" in central france, in the auvergne-rhone-alpes region, along the allier river.
[A]: vichy

[Q]: causality is a way to describe how different events relate to one another.
[A]: causality

[Q]: a state senator is a member of a state's senate, the upper house in the bicameral legislature of 49 u.s. states, or a legislator in nebraska's one house state legislature.
[A]:
state senator