Likewise, when words are stamped on the edge of a book (as is the case with most library books), these letters are separated when the book is opened, and this should not be done unless the book is urgently needed.
(The page has a reference to a note but I couldn't find the note.)
This made me wonder if you are erasing if the letters were not fully formed at the beginning of Shabbat, i.e. the book was already lying open. When you turn each page you're changing the state of the letters stamped on the sides, but they weren't whole to begin with so is there a problem of writing or erasing? If one really wants to read that library book or use a stamped reference book on Shabbat, does opening the book before Shabbat (in a way that it won't close on its own) let him do so?