Whirlwind

Whirlwind is a connection game for two players: Black and White. It is played on the intersections (points) of an even-sized square grid (board). The recommended board sizes are between 12×12 and 20×20 points. The top and bottom edges of the board are colored black; the left and right edges are colored white. At the start of the game, some black and white stones are arranged on the board in an interspersed pattern such that every stone (except those on the edges of the board) is a knight's jump away from four enemy stones and a large knight's jump away from four friendly stones. Only symmetrical setups are allowed. On every board size, two different symmetrical setups exist (see the pictures). Play Black plays first, then turns alternate. On your turn, place one or two stones of your color on empty points of the board. On their first turn, Black can only place one stone. At the end of your turn, for any two diagonally adjacent stones of your color there must be another stone of your color adjacent to both. You win by completing a chain of orthogonally connected stones of your color touching the two opposite board edges of your color. Draws are not possible. Notes The ban on diagonal connections as a means to prevent deadlocks on square connection games was introduced in Corey Clark's Slither.