Hint for Question 1.4 of Project 1

I am providing the results for a query similar to query 1.4. This may help you check whether you got the query right:

 List the authors having at least 20 papers, each of 
 which is directly cited by at least 20 other papers:

 Michael Stonebraker
 Jeffrey D. Ullman
 David J. DeWitt
 Philip A. Bernstein
 Won Kim
 Rakesh Agrawal
 Catriel Beeri
 Michael J. Carey
 Yehoshua Sagiv