Alpha-Beta Search

• A variation on minimax search that avoids provably useless subtrees in the search space.
• Alpha is the best possible outcome (initially -1)
• Beta is the worst that can happen (initially 1)
• Modifying minimax (successor generation loop):
  • Initial values for Alpha and Beta are taken from the parent node (-1, 1 for the starting node).
  • For each legal move m:
    • Generate a successor node (passing down current Alpha-Beta values)
    • If the current player is the protagonist, and successor's value is greater than Alpha, set Alpha to successor.
    • If the current player is the adversary, and successor's value is less than Beta, set Beta to successor.
    • If Alpha ≥ Beta, exit the loop.