return me the number of papers written by " H. V. Jagadish " and " Divesh Srivastava " before 2000 . 
return papers ;return #1 written before 2000 ;return #2 by H. V. Jagadish ;return #3 by Divesh Srivastava ;return number of  #4
['select', 'filter', 'filter', 'filter', 'aggregate']