Since Congress can and has retroactively changed the length of copyright repeatedly, I don't think that there's any presumption that you are buying a right to c

Since Congress can and has retroactively changed the length of copyright repeatedly, I don't think that there's any presumption that you are buying a right to copy after a given time, or at all. Since I'm against copyright in the first place, this argument about textbook copyright is rather academic to me. So to speak.