Liao, C., Guimbretière, F., Hinckley, K. (May 2005)
The affordances of paper (e.g., ease of annotation and navigation) make it a fundamental tool for knowledge gathering and crystallization tasks. During such tasks, users create a rich web of annotation and cross references. Un-fortunately, as paper is a static media, this web often gets trapped in the physical world. Some systems such as XLibris  address this problem by transferring this task in the digital realm where it is easy to capture all links created by the users. This approach is very powerful but suffers from the limitations of current tablet computers such as a limited screen space. In this paper we propose a paper-based interface to support the knowledge gathering and crystallization process. Our system considers document printouts as proxies of digital documents stored on the user's computer. Users can draw command gestures on printouts to indicate operations such a copying a document area, pasting an area previously copied, or creating a link. Upon pen synchronization, our infra-structure will execute these commands and present the result in our custom built viewer.