I remember my AI class working with chess engines, they all had to evaluate game trees using one or another heuristic strategy. The problem is that the search space is huge and so far a machine can only beat a Grand Master by evaluating millions of positions in advance... i.e. Deep Blue. As an example that these(brute force) techniques do not scale was given by John McCarthy http://www-formal.stanford.edu/jmc/reti.html This is why this could be quiet a breakthrough on chess AI and possibly other domains.