TwixT

TwixT is a two-player strategy board game, an early entrant in the 1960s 3M bookshelf game series. It became one of the most popular and enduring games in the series. It is a connection game where players alternate turns placing pegs and links on a pegboard in an attempt to link their opposite sides. The rules are simple but the strategy complex, so young children can play it, but it also appeals to adults. The game has been discontinued except in Germany.

TwixT was invented as a paper and pencil game in 1957 by Alex Randolph, a game designer. When Alex was commissioned along with Sid Sackson by 3M in 1961 to start a games division, the game was issued as a boardgame, one of the first 3M bookshelf games. Avalon Hill took over publication in 1976 when 3M sold its game division. Avalon's parent company was acquired by Hasbro in 1998, and the game was discontinued. The game is no longer produced in the United States, but a succession of German companies has produced the game since the 1970s under license from Avalon. Michael Katz, his nephew, owns the rights to Twixt since the death of Alex's widow, Gertrude Randolph. TwixT was short-listed for the first Spiel des Jahres in 1979, and was inducted into the Academy of Adventure Gaming Arts & Design's Hall of Fame, along with Randolph, in 2011.

Twixt is played on a board comprising a 24×24 square grid of holes (minus four corner holes). The playing pieces are pegs which fit the holes, and link pieces which join pegs along the diagonal of a 2×1 grid. In the 3M edition, players are Red and Black; different sets may use different colors. The topmost and bottommost rows of holes belong to the lighter color; the leftmost and rightmost rows to the darker color.

TwixT has been proven to be PSPACE-complete for determining the game value, via a reduction from Hex. TwixT has also been shown to be NP-complete for whether a single set of vertices can support a connecting path, via a reduction from 3-satisfiability. These proofs are indicative of a complex strategy: the game has not been solved, no winning strategy has been discovered, nor is the outcome of the game with perfect play known.

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