Conventions

This page lists possible conventions for Hex games. These conventions concern the color of the players, who goes first, the orientation of the board, and the numbering of the positions on the board. Unlike much older games such as Chess and Go, there are no universally agreed upon conventions for Hex, and different people, game sites, books, and computer programs sometimes use different conventions.

We distinguish logical from physical conventions. Logical conventions are concerned with the abstract rules of Hex, irrespectively of how the players visualize the game. Physical conventions relate to the specific appearance of the game board. When the game is played remotely, for example on an internet game server or over email, it is in principle possible for the two players to follow different physical conventions; for example, each player may choose their own preferred orientation of the board, or their own preferred colors for the pieces. However, both players should follow the same logical conventions.

Universal vs. local conventions

There are several aspects of a game of Hex that are arbitrary and do not affect game play in an essential way. This includes the orientation (rotation and reflection) of the board, the colors of the players, who goes first, which edge belongs to which player, and whether and how the cells on the board are numbered.

The same also applies to other games; for example, the game of Chess would not change in an essential way if the white square were in the bottom left corner instead of the bottom right one, if black went first instead of white, if the white queen started on a black square instead of a white one, if the ranks were lettered and the files numbered instead of the other way around, and so on.

In the case of established games such as Chess and Go, there are universal conventions that all players have agreed on. This has certain advantages. For example, every chess player understands what it means to move a white pawn from d2 to d4, without requiring further explanation.

In Hex, there are no universal conventions yet. Therefore, each player, book, game site, tournament, or hex program must define its own conventions. It may be desirable for a set of universal conventions to eventually crystallize.

Logical conventions

Cell naming

Cells are arranged in a grid, with each cell named by a letter and a number. Letters can be uppercase or lowercase. The following convention seems to be nearly universally used:

Convention: coordinate origin

Possible values:

• Acute: The cell A1 is an an acute corner of the board.

In particular, this means that the three cells A1, B1, and A2 are all adjacent to each other.

For the purpose of the following exposition, it is useful to refer to the cells that share a common number as a "rank", and to the cells that share a common letter as a "file", as in Chess. For example, the 1-rank consists of the cells A1, B1, C1, etc., and the A-file consists of the cells A1, A2, A3, etc.

Edge coloring

To avoid referencing specific physical attributes of the game, we will refer to the color of the first piece played in the game as "color 1", and to the other color as "color 2". One pair of opposite edges "belongs to" color 1; these are the edges that the player who is playing color 1 is trying to connect. The other pair of opposite edges belongs to color 2.

Convention: edge coloring

Possible values:

• Normal: The edge that is adjacent to the 1-rank belongs to color 1, and the edge that is adjacent to the A-file belongs to color 2.

In other words, the normal edge coloring convention states that the color 1 edges are parallel to ranks, and the color 2 edges are parallel to files. In a typical rendering of the board, the letters (naming files) are written along the color 1 edge and the numbers (naming ranks) are written along the color 2 edge.

I am not aware of anybody who has used the opposite convention. However, there are some authors who use no edge coloring convention at all.

Swapping

There are two different ways of implementing the swap rule. Which convention is chosen will affect the notation for games. It is also possible to permit both methods of swapping; then it is up to the player to decide which method to use.

Convention: swap method

Possible values:

• Swap sides: Upon playing a swap move, the board position stays the same and the players change colors.

• Swap pieces: Upon playing a swap move, the players keep their colors and the board position is mirrored (ranks and files interchanged) and the color of the pieces is inverted. For example, a black piece at A2 would be replaced by a white piece at B1.

Here is an example using the swap sides convention: Player 1 plays a black piece at g4. Player 2 swaps sides. The board state remains unchanged, and immediately after the swap, it is player 1's turn to play a white piece.

Here is an example using the swap pieces convention: Player 1 plays a black piece at g4. Player 2 swaps pieces, and replaces the black piece at g4 with a white piece at d7. Immediately after the swap, it is player 1's turn to play a black piece.

When using algebraic notation for a sequence of moves, it is important to know which swap method was used. The swap method should either be defined for the context in which it is used, or else the notation should state explicitly which method was used. For example, with the swap sides convention, the notation "g4 swap f7 e7" means player 1 plays color 1 at g4, player 2 swaps, player 1 plays color 2 at f7, and player 2 plays color 1 at e7. With the swap pieces convention, the same game would be described as "g4 swap g6 g5". Here, player 1 plays color 1 at g4, player 2 replaces this by a piece by color 2 at d7, then player 1 plays color 1 at g6 and player 2 plays color 2 at g5. It is best not to use ambiguous notation at all; the two games can then be denoted "g4 swap-sides f7 e7" and "g4 swap-pieces g6 g5".

Note that the above logical conventions are purely symbolic. They do not depend on any particular board layout.

Passing

Although passing (skipping a move) is not always considered part of the classic Hex rules, allowing it does not change the nature of the game and has certain advantages. See the page on passing for more details.

Convention: passing

Possible values:

• Explicit: Players can pass and there is an explicit passing move in the game record, e.g.: "Black passed".

• Implicit: There is no explicit passing move, but a player can move twice in a row (presumably when the other player allows it).

• None: Moves must be strictly alternating and passing is not allowed.

Physical conventions

Colors

The most common color schemes are:

• Black and white.
• Red and blue.
• V and H.

With each color scheme, there are two possible conventions to which color is color 1. The more common conventions seem to be "black goes first", "red goes first", and "V goes first", but the opposite conventions also exist.

Board orientatation

The board can be oriented in a number of different ways. It can be oriented in the positive or negative senses, and rotated to various angles.

Convention: board sense

Possible values:

• Positive: The cells A1, B1, A2 form a clockwise triangle in that order.

• Negative: The cells A1, B1, A2 form a counterclockwise triangle in that order.

The positive sense can also be described by saying that if the board is rotated so that A1 points west, then the ranks run from southwest to northeast, and the files run from northwest to southeast. This convention can also be described as "letters above numbers", because if A1 points left, the letters A,B,C marking the files appear above the numbers 1,2,3 marking the ranks.

Convention: board rotation

There is probably no need for a preferred board rotation; indeed, players using a physical game board may freely move around the board and look at it from any angle they want.

In computer hex, the most common board rotations are:

• Diamond: the A1 corner points west, i.e., in the direction of 9 o'clock on an analog clock.

• Flat: the A1 corner points northwest, i.e., in the direction of 10 o'clock.

• Flat II: the A1 corner points southwest, i.e., in the direction of 8 o'clock.

The following table illustrates some common board layouts. Here, color 1 is shown as black and color 2 is shown as white.

Positive diamond	Positive flat	Positive flat II
Negative diamond	Negative flat	Negative flat II

List of conventions used

	Origin	Edge coloring	Swap	Passing	Colors	First player	Orientation
Browne	acute	normal	sides	N/A	black/white	black	positive diamond
Seymour	acute	normal	pieces	explicit in puzzles, none in book	black/white	black	positive diamond
Berge	acute	normal	?	N/A	black/white	white	negative flat II
Hayward and Toft	acute	?	sides	N/A	black/white	any	diamond
Hexy	acute	normal	pieces	none	red/blue	red	positive diamond / positive flat / negative flat II
Mohex	acute	normal	N/A	implicit	black/white	black	positive flat
HexGui	acute	normal	both	implicit	black/white	black	any
Board Game Arena	acute	normal	pieces	explicit	red/blue	red	positive flat
Little Golem	acute	normal	pieces	none	black/white	black	positive flat
igGameCenter	acute	normal	sides	none	red/blue or black/white	red or black	positive flat
PlayOK	acute	normal	pieces	none	black/white	black	positive flat
HexWorld	acute	normal	both	explicit	black/white or red/blue	black or red	any positive
TRMPH	acute	normal	N/A	none	black/white	black	positive flat
HexWiki	acute	normal	both	N/A	red/blue	red	positive flat

Notes:

• Browne states that there is no universal convention for which color goes first, but black goes first in all examples in the book.

• Berge states that any player can go first, but white goes first in his example games.

• TRMPH implements swapping incorrectly. It changes the color of the piece, but not its location.

• MoHex does not seem to implement swapping.

• BoardGameArena has an explicit passing move, but three consecutive passes are not allowed. Therefore, if a player passes, the opponent can effectively reject the pass by passing too.