M. Rashid, U. Uzma-Muhmood, and A. Ayse-Gulmez. Proceedings of the 9th WSEAS international conference on Distance
learning and web engineering, page 29 -- 37. Stevens Point, Wisconsin, USA; WSEAS, World Scientific and Engineering Academy and Society, (2009)
N. Peirceand, O. Conlan, and V. Wade. Second IEEE International Conference on Digital Games and Intelligent
Toys Based Education, page 28 -- 35. (2008)