Mathematics here . and I ' ve started looking for books in the free domain . For example , my next semester Calculus class is going to be using a free book that I found in the public domain . I haven ' t decided which of the two that I ' m going to primarily use yet , but yeah . both of the ones that I ' m waffling between is open to the free use of anyone . I just don ' t see how charging my students for an expensive textbook is important , particularly with the information in the classes that I teach primarily fundamental stuff like basic Calculus , Linear Algebra , College Algebra , and the like hasn ' t changed in years and years . Of course , I will comment that even though I ' m a Visiting Professor at the school where I am , I ' m given complete freedom in the planning and creationpedagogy of my classes , so I have no pressure from anyone other than myself sometimes the bookstore if they ' re having issues stocking an older edition .