@inproceedings{
author={Karhulahti Veli-Matti},
year={2014},
title={Puzzle Is Not a Game! Basic Structures of Challenge},
isbn={ISSN 2342-9666},
booktitle={DiGRA \&\#3913 - Proceedings of the 2013 DiGRA International Conference: DeFragging Game Studies},
month={August},
url={http://www.digra.org/wp-content/uploads/digital-library/paper_179.pdf}
}