L. von Ahn, and L. Dabbish. CHI '04: Proceedings of the SIGCHI conference on Human factors in computing systems, page 319--326. New York, NY, USA, ACM, (2004)
S. Hacker, and L. von Ahn. CHI '09: Proceedings of the 27th international conference on Human factors in computing systems, page 1207--1216. New York, NY, USA, ACM, (2009)
L. von Ahn, and L. Dabbish. CHI '04: Proceedings of the SIGCHI conference on Human factors in computing systems, page 319--326. New York, NY, USA, ACM Press, (2004)
L. von Ahn, and L. Dabbish. CHI '04: Proceedings of the SIGCHI conference on Human factors in computing systems, page 319--326. New York, NY, USA, ACM Press, (2004)