Yamaguchi rule
- The first player puts one of the 26 openings and declares how many 5th moves will be offered in that game.
- The next player has a right to swap.
- The white player puts the 4th move anywhere on board.
- The black player puts as many 5th moves on the board as it was declared before (symmetrical moves not allowed).
- The white player chooses one 5th from these offerings and plays the 6th move.