referred to a 'flash of a suggestion' which came to Mr. Nash from a Danish source, and which he later forgot about. It seems the most likely explanation." Published games Initially in 1942, Hein distributed the game, which was then called Polygon, in the form of 50-sheet game pads. Each sheet contained an empty 11x11 empty board that could be played on with pencils or pens. In 1952, Parker Brothers marketed a version of the game under the name "Hex", and the name stuck. Parker Brothers also sold a version under the "Con-tac-tix" name in 1968. Hex was also issued as one of the games in the 1974 3M Paper Games Series; the game contained a 50-sheet pad of ruled Hex grids. Hex is currently published by Nestorgames in a 11x11 size and a 14x14 size. Shannon's Hex machine About 1950, Claude Shannon and E. F. Moore constructed an analog Hex playing machine, which was essentially a resistance network with resistors for edges and light bulbs for vertices. The move to be made corresponded to a certain specified saddle point in the network. The machine played a reasonably good game of Hex. Later, researchers attempting to solve the game and develop Hex-playing computer algorithms emulated Shannon's network to create strong computer players. Research timeline It was known to Hein in 1942 that Hex cannot end in a draw; in fact, one of his design criteria for the game was that "exactly one of the two players can connect their two sides." It was also known to Hein that the first player has a theoretical winning strategy. In 1952 John Nash wrote up an existence proof that on symmetrical boards, the first player has a winning strategy. In 1964, the mathematician Alfred Lehman showed that Hex cannot be represented as a binary matroid, so a determinate winning strategy like that for the Shannon switching game on a regular rectangular grid was unavailable. In 1981, the Stefan Reisch showed that Hex is PSPACE-complete. In 2002, the first explicit winning strategy (a reduction-type strategy) on a 7×7 board was described. In the 2000s, by using brute force search computer algorithms, Hex boards up to size 9×9 (as of 2016) have been completely solved. Starting about 2006, the field of computer Hex came to be dominated by Monte Carlo tree search methods borrowed from successful computer implementations of Go. These replaced earlier implementations that