On SQuAD1.1 where the best models already outperform humans, questions remaining unsolved are really difficult ones.
given passage P = {p i } m i=1 and question Q = {q j } n j=1 , we first pack them into a single sequence of length m + n + 3, i.e., where SEP is the token separating Q and P , and CLS the token for classification (will not be used in this paper).