PDF software to read many documents side-by-side in iPad? This thread is a part of the major thread about using iPad for education purposes here.

When I do my homework, I often need to recap lecture notes and at the same time do assignments. Before my printer broke, I printed everything -- now with my iPad, I use only the screen. The problem is that I have only one iPad and so I am looking for a software using which I could read many PDFs at the same time. Does such a PDF reader exist?

I have used PDF Expert but it lacks this feature. I have also tried apps such as iAnnotate but cannot find this feature.
Side by Side allows you to read up to 4 different PDFs side by side on an iPad.