| Challenges 99 | Challenges 2001 | |
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| Challenges 2001 Website | ||
| Conference Proceedings | Conference Proceedings | |
| Challenges 2003 | Challenges 2005 | |
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| Challenges 2003 Website | Challenges 2005 Website | |
| Conference Proceedings | Conference Proceedings | |
| Challenges 2007 | ||
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| Challenges 2007 Website |