After reading 1984, I was asked by my teacher to prove I exist. How can I do so?

After the thorough
brainwashingreceives in this novel, this question is sensible. Winston loses power over his own
thinking which is like losing ownership of his existence and ownership of himself. 

Yet Winston, as a character, exists with certainty because he is experiencing the
events of the novel. He has a mind to be brainwashed. 

This type of proof of
existence is drawn from the famous philosophical treatise of Rene Descartes, the...