impetus

A rule explained in a minute, and a depth that lasts for years: that is what makes chess or go. Impetus tries to head in that direction, without claiming to get there.

The rule fits in three sentences. On a nine-by-nine board, each player has ten stones in reserve and takes a single action per turn: place a stone on their starting row, or slide one, straight, three squares at most, up to the first obstacle. An enemy stone is captured; a friendly stone or an edge stops it dead. You win by surviving one turn on the opponent’s row, by capturing everything, or by leaving the opponent no legal move.

The rest is tuning, and tuning is not done by feel. The first version allowed unlimited sliding: autoplay showed black crossing the empty board on their second move and winning trivially. Hence the range of three, which makes blocking central again. The breakthrough then became deferred, a stone arriving on the opponent’s row having to survive one reply, which lengthened games by a good third and brought out real defence: double threats, protected sacrifices.

The variant sweep also settled open questions: nine-by-nine, reserve of ten, range of three is the only balanced configuration among those tested; there is no draw; the repetition rule guarantees termination; no forced win at the opening was detected at depth thirteen. The slight remaining bias, around 55/45, awaits the only judge still missing: human games.

Two neighbouring prototypes explore the same idea through other doors, and remain concepts. Ombre replaces capture with territory: each stone projects its influence in four directions up to the first obstacle, and a square belongs to the side that covers it most. Détour keeps the race and the walls, but makes the walls destructible, so that you can never be blocked for good, and sends the pawn you bump into back to its starting point. Impetus remains the main project of the three.