Division operator in Relational Databases

Yesterday before submitting my assignment of the database, which was totally related to relational algebra queries, i got stuck in Division operator. I read the text book of Connolly “Introduction to Database System” But the formulas got me confused. Then eventually I’ve just got a copy of THE MANGA GUIDE TO DATABASES (ISBN 978-1-59327-190-9); it is one of a series of “Manga Guides” (the others are Calculus and Statistics).  Since I consider myself a long [...]