The game of Hex was invented and popularized in Denmark by Piet Hein in 1942, and later independently rediscovered by John Nash in 1947. The game is attractive because it has extremely simple rules, yet a surprising amount of strategic depth. Another interesting aspect is that the game can't end in a tie.
The board has two red edges and two blue edges. Each player's goal is to connect their two edges by stones of their color.
The players alternately place a stone of their own color on the board, with Red going first. A stone can be placed on any empty cell. Once placed, stones are never moved or removed.
THE SWAP RULE
To make sure the first player does not have an unfair advantage, the swap rule is used. After the first player opens with a red stone, the second player can either
- continue to play normally, by placing a blue stone, or
- decide to switch colors. In that case, the second player becomes Red, the first player becomes Blue, and the first move is kept. After this, the game continues normally, i.e., it is the first player's turn to play a blue stone.
Alternatively, the swap rule can also be implemented in such a way that the players keep their original colors. In that case, if Blue wants to swap, Red's initial stone is replaced by a blue stone and mirrored about the long diagonal. After this, it is Red's turn.
The game ends when one of the players has connected their edges with a path of stones of their color. The game can't end in a tie. It is customary for the losing player to resign when it is clear to both players who will win.
The game can be played on boards of several different sizes. The 6x6 board is designed to help beginners understand the basic rules and discover simple game patterns. The 11x11 board is a more classic size and was used by Piet Hein. The 13x13 board is preferred by many experts. The 14x14 board was recommended by John Nash, and the 15x15 board allows even longer plays.