Alpha and Beta values
M?x node has ? value
- the alpha value is lower bound on the exact minimax score
- with best play M ?x can guarantee scoring at least ?
Min node has ? value
- the beta value is upper bound on the exact minimax score
- with best play Min can guarantee scoring no more than ?
At Max node, if an ancestor Min node has ? < ?
- Min’s best play must never let Max move to this node
- therefore this node is irrelevant
- if ? = ?, Min can do as well without letting Max get here
- so again we need not continue