Computing & AI · the experiment
Replay go under superko
A rule that forbids recreating any earlier position, a solver that keeps its shortcuts honest, a 4×7 board that loses 16 points. Four questions, from beginner to expert.
1 · Understand the rule
Beginner
Why does superko make a go board so hard to solve?
2 · Measure the shortcut
On the 3×7 board, without proof transfer, the solver takes 664 billion steps. With it, 112 million, for the same value.
Intermediate
By how much does proof transfer divide the work?
3 · Transfer a proof
The solver has stored a proof that Black wins from a position. It reaches that position again by another path, on which a position that only White had to recreate has already appeared.
Expert
Does the proof still hold on this path?
4 · Find the 4×7 flaw
On 4×7, after move 25, White plays G2 instead of A2. White ends up capturing a stone in a ko. Under the old rule, a pass would lift the ban: Black would retake and win the whole board.
Expert
Under superko, why can Black not retake?
Board solved
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