How to read a card
- A card is a claim (A, T, h). If Maker owns every X and Breaker owns no cell of the drawn region, Maker wins within h more moves.
- Maker claims the gray pivot. After that, Maker owns every X on every child board. The blue outline on a child board marks this pivot.
- Breaker's reply blocks exactly the children whose envelope contains it. Cells common to every child envelope already belong to Maker, so at least one child survives.
- Maker continues with the first surviving child in the certificate's order. Its height is at most h − 1.