Solving 2x2 go
This program solves the game of Go played
on a 2x2 board using area rules and positional superko.
It demonstrates the enormous importance of good move ordering in
exhaustive alpha beta search.
With the given ordering of passing last, as many as
19397529 nodes are searched, up to a depth of 58. But
putting passes first
requires the search of only 1446 nodes, to a depth of no more than 22.
Minimax, which doesn't depend on move ordering, takes over a week
while searching a few trillion nodes.