Reducing the figure of thirty to a mere two for the sake of a diagram, the player (White) making a three-move look-ahead is confronted by a 'tree' such as:
为了简化图表，我们把30种着法减少为2种，白方如果要往前看三步，那么就面临这样的一棵树：
Current position, W to play
当前局面，白方走棋
Position resulting from the 2 possible W moves
白方的2种着法会导致的局面
Position resulting from the possible replies
黑方的着法会导致的局面
Position resulting from the possible W replies.
白方的着法会导致的局面
These positions are evaluated by scoring.
对这些局面用分数进行评估
A human playing White might reason that it would be good to reach position E, but Black will not be so obliging, and will respond to move B by reply F.
白方可能会认为，到达E是最理想的，但黑方不会这么乐于助人，如果白方走到B，那么他就会回应F。
A second best, for White, would be position D, but again it must be assumed that Black will play C to prevent this.
对白方而言，第二好的选择是D，但同样可以想见，黑方会走到C来避免D。
Of the two evils, positions C and F, C is the lesser one, since at least it guarantees for White a position of value 27. So White plays move A.
在这两个不幸中，C和F局面相比，C的危险性更小一些，因为它能使白方保证至少达到价值为27的局面。因此白方会进行A移动。
A 'machine' could simulate this train of thought by a method of 'backing up' the tree.
机器可以通过推导这棵树，来模拟这一系列想法。
Having worked out all the scores for three moves ahead, it would then label the intermediate positions on a minimax basis.
对三步之后的各种局面进行评估之后，根据最大值最小化的思想，对中间各层的局面进行标示。
It would assign 27 to C, 45 to D, 81 to E, 16 to F (the best in each case), then 27 to A, 16 to B (the worst in each case), and finally select move A for White.
它会将C标为27, D标为45, E标为81, F标为16（每个下面的最好局面），然后将A标为27, B标为16（每个下面的最坏局面）。