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.

doriva (born 28 may 1972) is a former brazilian football player.
doriva

a mathematician's apology is a book about mathematics which was written in 1940.
a mathematician's apology

quechuas is the term used for several ethnic groups in ̈south america that use a quechua language (southern quechua mainly).

quechuas