ALPHA-BETA PRUNING In the course of a depth-first search of the game-tree, we may sometimes recognize that certain sub-trees do not need to be explored. For instance, once we begin to explore the sub-tree rooted at C, and find that position G has value 1, we know that the minimax value of position C will be 1 or smaller. Since the minimax value of position B has already been computed to be 4, which is larger than 1, we do not need to evaluate positions H and I; we can conclude, on the basis of the information we already have, that the minimax value of A is 4, and that the correct minimax move is from A to B. A / \ / \ Computer's move / \ 4 C / | \ / | \ / | \ / | \ Human's move / | \ / | \ 4 5 6 1 ? ? Ignoring sub-trees in this fashion (a process called alpha-beta pruning) is easily implemented on a computer, and can lead to dramatic speed-up of depth-first searches.