Otmar Hilliges Shahram Izadi Andrew D. Wilson Steve Hodges Armando Garcia-Mendoza Andreas Butz Interactions in the air: adding further depth to interactive tabletops. 139-148 2009 UIST http://doi.acm.org/10.1145/1622176.1622203 conf/uist/2009 db/conf/uist/uist2009.html#HilligesIWHGB09