The algorithm stores intervals for nodes of the tree as opposed to single point-valued estimates.
If all intervals attached to leaf nodes satisfy this property, then B* will identify an optimal path to the goal state.
B* is a best-first process, which means that it is very efficient to traverse the tree, repeatedly descending to find a leaf to expand.
(Note: Whether or not the tree is memory-resident, is a function of the overall implementation efficiency, including how it may be mapped and/or managed via real or virtual memory.)
When transpositions are possible, then the back-up operation might need to alter the values of nodes that did not lie on the selection path.
Note that propagation can cease when a backup operation does not change the interval associated with a node.
The Maven (Scrabble) program has an innovation that improves the robustness of B* when evaluation errors are possible.
Equivalently, you can represent all intervals from the perspective of the side to move, and then negate the values during the back-up operation.
There is no report of how well this system performed compared to alpha–beta pruning search engines running on the same hardware.