Two years ago, when Lenovo first unveiled the futuristic Yoga Book, the company held it up alongside a hardcover Dr. Seuss book to demonstrate how thin and light it was. It had a “Halo” keyboard: a bottom half that lit up to create a digital keyboard. You could write directly on this keyless keyboard, too, as though it was a notepad. It was a whole lot of new tech packed into a tiny, $500, fold-over tablet, but not all of that tech was fully-baked.