Rafael Ballagas Sven G. Kratz Jan O. Borchers Eugen Yu Steffen P. Walz Claudia O. Fuhr Ludger Hovestadt Martin Tann REXplorer: a mobile, pervasive spell-casting game for tourists. 1929-1934 2007 conf/chi/2007a CHI Extended Abstracts http://doi.acm.org/10.1145/1240866.1240927 db/conf/chi/chi2007a.html#BallagasKBYWFHT07