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.

[EX Q]: he wrote under the pen name d. h. lawrence.
[EX A]: d. h. lawrence

[EX Q]: hiromasa yamamoto (山本浩正, yamamoto hiromasa, born 5 june 1979) is a japanese professional athlete.
[EX A]: hiromasa yamamoto

[EX Q]: the informal economy is that part of economy which is not reported in official statistics such as the gross domestic product of a country.
[EX A]:
informal economy