I beg you to consider in the bowels of your library that the ereader may be a mutation of the book that masks itself by taking on some of the properties of its bitty foe. I of course refer to the ereader that does not have any sort of connectivity other than that of the host womb. The magic hour is 1941 for legal download which means that Virginia Woolf is on, Jacob's Room, The Voyage Out, the hilarious miserabilism of Gissing The Private Papers of Henry Ryecroft, the marvellous Kierkegaard vs Regina in his Journals and the Michelmas Geese.
All this and more in a platen that I can shove in my coat pocket.
Add to that the capacity to 'underline' and to substitute for the sheaves of post-its that fatten the great texts eg. the table talk of S.T.C. and I think we have an 'extension' that is virtually prosthetic.