>The main UX challenge that I haven't found anything has really solved yet is the ability to show 2 or more pages at once (and do so in a way that's simple & in

>The main UX challenge that I haven't found anything has really solved yet is the ability to show 2 or more pages at once (and do so in a way that's simple & intuitive). Also related is some way to mimic the ability to, with a textbook, stick a pen or finger in between two pages as a "temporary bookmark", to make it easy to flip back & forth. Maybe a spot on the screen or a button on the side you can press to bounce to some "reference" bookmark, letting you navigate there normally until you release it, at which point you instantly return to the page you were reading.