In the references list (usually at the end of a book), I've noticed that authors like to include references to other materials. However these materials are not so-called "referenced" or "linked" at all throughout the entire book.
I was wondering why did they put that list there? Are they required to put a list of references for materials they have referred to and adopted information from?
Per the replies, I'm actually particularly interested in: Do we have to inform the authors of those books/materials, that we have the title of their books in our "bibliography" section ?