There are two semantics inside an Alpha-Beta like search, related to Upper Bounds:
- Beta is an Upper Bound of a score for this node.
- An Upper Bound is returned from an Alpha-Beta like search, if it fails low. All moves were searched, but none improved alpha. The node searched was a confirmed All-Node.
- Using just Upperbounds and Lowerbounds by Alvaro Jose Povoa Cardoso, CCC, February 01, 2001
- bound type in PVS ? by Mahmoud Uthman, CCC, January 23, 2017 » Bound, Exact Score, Principal Variation Search