For somebody who tries never to make hardcopies of anything, I seem to spend a lot of time thinking up ways to improve computer printer performance.
In order to save on the amount of paper that’s wasted, today’s invention is white ink. One’s printer will create a set of human-undetectable marks on every printed page. When that page is returned to the feed tray, it will be identified and the white ink applied, like Tippex, to the pre-existing letterforms (whose precise locations etc will have been stored in printer memory).
This whiting-out could occur in realtime ie with one old letter being ‘snowpaked’ over just before the new one is printed. Thus a single sheet of paper could be reused multiple times -as in a medieval palimpsest.