I would like to create a course that use a well known book in my circle of expertise and that of students. Is it ok to create a course that needs the purchase of a book? The book is not written by me, and I have no affiliation with the author, nor get any commissions etc. The book is simply the best one I found on the subject and a course on how to practice it's content, I think would be very valuable. The book costs about 10-15 dollars new, used can be found on amazon for a couple of bucks. It's an old book that was written in the early 90's but it's as good as ever.