Consider the following relational model:

COURSE(coursenr, coursename, profnr) – profnr is a foreign key referring to profnr in PROFESSOR

PROFESSOR(profnr, profname)

PRE-REQUISITE(coursenr, pre-req-coursenr) – coursenr is a foreign key referring to coursenr in COURSE; pre-req-coursenr is a foreign key referring to coursenr in COURSE 

The PRE-REQUISITE relation essentially models a recursive N:M relationship type for COURSE, since a course can have multiple prerequisite courses and a course can be a prerequisite for multiple other courses.

Write a recursive SQL query to list all prerequisite courses for the course “Principles of Database Management”.