@INPROCEEDINGS{Streit2009,
  author = {Marc Streit and Hans-J{\"o}rg Schulz and Dieter Schmalstieg and Heidrun
	Schumann},
  title = {Towards Multi-User Multi-Level Interaction},
  booktitle = {Workshop on Collaborative Visualization on Interactive Surfaces (part
	of VisWeek'09)},
  year = {2009}
}