26. Probabilistic Alpha-Beta Pruning

INSTRUCTOR NOTE:

Note: In the topmost (root) node of the tree, you may drop the inequality sign (here a lower bound, e.g. reduce >=7 to 7) after you've gone through all the sub-trees, or you may leave it in.

For the purposes of alpha-beta pruning, a lower bound is sufficient for a MAX node, because if you need to choose among sibling MAX nodes at the same level, you only need to pick the one with the greatest lower bound. Similarly, for MIN nodes you pick the one with the least upper bound.