SSS* = Alpha-Beta + TT
  In 1979 Stockman introduced the SSS* minimax search algorithm that domi-
nates Alpha-Beta in the number of leaf nodes expanded. Further investigation of
the algorithm showed that it had three serious drawbacks, which prevented its
use by practitioners: it is difficult to understand, it has large memory
requirements, and it is slow. This paper presents an alternate formulation of
SSS*, in which it is implemented as a series of Alpha-Beta calls that use a
transposition table (AB- SSS*). The reformulation solves all three perceived
drawbacks of SSS*, making it a practical algorithm. Further, because the search
is now based on Alpha-Beta, the extensive research on minimax search
enhancements can be easily integrated into AB-SSS*. To test AB-SSS* in
practise, it has been implemented in three state-of-the- art programs: for
checkers, Othello and chess. AB-SSS* is comparable in performance to Alpha-Beta
on leaf node count in all three games, making it a viable alternative to
Alpha-Beta in practise. Whereas SSS* has usually been regarded as being
entirely different from Alpha-Beta, it turns out to be just an Alpha-Beta
enhancement, like null-window searching. This runs counter to published
simulation results. Our research leads to the surprising result that iterative
deepening versions of Alpha-Beta can expand fewer leaf nodes than iterative
deepening versions of SSS* due to dynamic move re-ordering.
