Incursion Go is a Go variant where standard ko rules are not used. Instead, it is illegal to make an incursion if your opponent's last move was an incursion.
An incursion is a placement in an enemy territory. A territory is an empty point along with all points one can reach from it through a series of steps onto orthogonally adjacent empty points. An enemy territory is a territory such that all stones orthogonally adjacent to points in the territory are of your opponent's color.
All other rules are the same as in Go. Suicide of one or more stones is not allowed, and area scoring is used.
All known forced Go cycles are impossible in this variant. Unlike the related variant Stoical Go, Incursion Go preserves snapbacks.
If you place a stone on your turn and, by the end of it, the board position is the same as the board position at the end of any of your previous turns, the game ends in a draw. However, if forced cycles are impossible, this will require cooperation between the players, which should not occur in actual play. However, if forced cycles are impossible, this will require cooperation between the players, which should not occur in actual play.
In a more radical, less restrictive implementation of this idea, an incursion is said to be minimal if it captures exactly zero or one groups, and it is illegal to make a minimal incursion if your opponent's last move was a minimal incursion. Non-minimal incursions are always legal. This also prevents all known forced cycles.
Luis Bolaños Mures designed Incursion Go in April 2023.
is an incursion, Black cannot reply with another incursion at the vital point a, but must make a ko threat first, which must itself not be an incursion. Once Black runs out of ko threats, the black group will die.
and those ko threats are all incursions.