title: Relational algebra, without use of division operator
body: <p>Given :</p>
  
  <pre><code>PROFESSOR(NAME,OFFICE,DEPARTMENT,AGE)
  COURSE(CNO,TITLE,DEPARTMENT)
  ENROLL(CNO,SEMESTER,INSTRUCTOR_NAME,ENROLLMENT)
  </code></pre>
  
  <p>Find names of professors who taught all the courses in their department. Your solution must not use the division operator.</p>
  
  <p>Is this question solvable using relational algebra? </p>
  
  <p>I feel that this is not possible, even with the use of division operator. Unless we do it repeatedly for each professor name or for a particular department.</p>
  
  <p>Any great ideas?</p>