Calculating beta values
At a Min node
- after we obtain the final backed up value of the first child
- we can set ? of the node to this value
- when we get the final backed up value of the second child
- we can decrease ? if the new value is smaller
- when we have the final child, or if alpha cutoff occurs
- the stored ? becomes the final backed up value
- only then can we set the ? of the parent Min node
- only then can we guarantee that ? will not decrease
Note the difference
- setting beta value of current node as we go along
- vs. propagating value up only when it is finalised