These "solvers" compete to meet thorny technical challenges posted by "seeker" companies.

Perhaps the thorniest challenge is to break the cycle of violence in Afghanistan.

So the drug traffickers are faced with the thorny challenge of physically repatriating their profits.

The report on commercial garbage comes as the city's trash policy, one of the thorniest challenges for generations of public officials, is again in flux.

Mr. Goldberg acknowledged that he faced a thorny challenge.

But in the short term, China's march into the World Trade Organization will pose a thorny challenge.

But expanding to a factory posed some thorny challenges.

Both sides need to devote creative thinking into how we might address these thorny challenges.

The approach is aimed at using light to improve timing, an increasingly thorny challenge for the makers of the largest and most powerful silicon chips.

Given the thorny challenges ahead, it is not clear investors are all that concerned about the nationality of the top management.