REFERENCES
- Caillois , R. 1961 . Man, play, and games , New York : Free Press .
- Huizinga , J. 1950 . Homo ludens: A study of the play element in culture , London : Routledge & Kegan .
- Koster , R. 2010 . A theory of fun . http://www.theoryoffun.com/theoryoffun.pdf (accessed September 20, 2010)
- Piaget , J. 1962 . Play, dreams and imitation in childhood. , New York : Norton .
- Sutton-Smith , B. 2001 . The ambiguity of play , Cambridge, MA : Harvard University Press .