<p>Some professors may be required by their department to have, officially, SomeBookX. However, SomeBookX may really be a useless book of very little value, but the department head/undergrad studies/book committee likes it/owes a favor to the publisher/author. Thus, all Hamsterology classes must use SomeBookX “officially,” and the professor must list it on the syllabus, but he/she may simply not use it because they don’t “have time.”</p>