N. Patel, and L. Sethi. Proceedings of the SPIE on Storage and Retrieval for Still Image and Video Databases, 2670, page 373--384. San Jose, USA, (1996)
C. Woo, J. Choi, and M. Evens. Proceedings of the 6th International conference on Intelligent Tutoring
Systems, Biarritz, France and San Sebastian, Spain, (2002)