How many papers were written by authors who cooperated with University of Hong Kong?
University of Hong Kong' is an affiliation
SELECT COUNT(T2.PaperId) FROM Author AS T1 INNER JOIN PaperAuthor AS T2 ON T1.Id = T2.AuthorId WHERE T1.Affiliation = 'University of Hong Kong'
database name:db_id authors
Author table Author Cols: Id dtype integer, Name dtype text, Affiliation dtype text, 
Conference table Conference Cols: Id dtype integer, ShortName dtype text, FullName dtype text, HomePage dtype text, 
Journal table Journal Cols: Id dtype integer, ShortName dtype text, FullName dtype text, HomePage dtype text, 
Paper table Paper Cols: Id dtype integer, Title dtype text, Year dtype integer, ConferenceId dtype integer, JournalId dtype integer, Keyword dtype text, 
PaperAuthor table PaperAuthor Cols: PaperId dtype integer, AuthorId dtype integer, Name dtype text, Affiliation dtype text, 
