Irensei (囲連星) is played on a 19×19 Go board, with Go stones, and Go capturing rules, and Go ko rules, but with one significant difference: the goal is not to surround territory, it is to get 7-in-a-row in the central 15×15 region. A winning 7-in-a-row can be either orthogonal or diagonal, but it must be a straight unbroken line of friendly stones

The two colors are traditionally Black and White for P1 and P2 respectively, but the default P1 and P2 colors on AP are Red and Blue respectively. This page will therefore use “Black/Red” and “White/Blue” to refer to the players

See n-in-a-row games for more information on the family it belongs to, as well as explanations of some things common to them, such as certain pie rules

• Designer: Toki Higashi
• Coder: ypaul
• Irensei at BoardGameGeek
• Irensei at Wikipedia
• Irensei at Online Go Forums
• Irensei at 日本囲連星協会 (primary source)

• The goal is to form a 7-in-a-row within the central 15×15 region
  • Stones in the gutter (ie, outside the central 15×15 region) do not count toward forming a winning 7-in-a-row
  • The 3rd line counts as part of the central 15×15 region
  • If both players pass in succession, the game is a draw
    • Exception: AP offers a variant “Pass tiebreak”, in which the first player to pass wins once both players pass in succession
• Go rules apply
  • Capture strings (contiguous orthogonally connected sets of like-colored stones) by removing their last liberty (empty point orthogonally adjacent to at least one stone in the string)
  • Suicide is forbidden (placing a stone which does not capture any opposing string but is itself captured because it does not have any liberties)
    • Exception: if the placement would immediately win, it is legal and wins. In other words, the winning condition is checked before the capture condition
  • The Ko rule is used (specifically Situational Superko: don't repeat a board position with the same player to play)
    • tldr: you can't undo your opponent's last move. That's virtually always all you need to know

Overlines in n-in-a-row games refer to getting strictly more stones in a row than necessary to win (eg, 8 or more in Irensei since 7-in-a-row is the goal). Some games allow players to win via an overline, in other games making an overline neither wins nor loses but the game continues, and in other games making an overline is not a win but a loss (or illegal)

In Irensei, stones anywhere on the board, even in the gutter, count towards overlines. This means that a position might appear to be a win looking only at the central 15×15 region, but actually be a loss by illegal overline because of stones in the gutter. AP offers three overlining rules as variants

• Asymmetric overline
  • If Black/Red forms an overline, they lose
  • White/Blue is allowed to form overlines, and the stones in them can contribute to a winning 7-in-a-row
• Symmetric overline win
  • Both players are allowed to form overlines, and the stones in them can contribute to a winning 7-in-a-row
• Symmetric overline loss
  • An overline by either player is a loss/illegal for them

Asymmetric overline is the official rule and aims to balance the game thereby

Pie rules serve not only to balance the first player advantage present in many games, but also to increase opening variety and limit the power of opening preparation. The metaphor is of one person slicing a piece of pie into two slices, and letting the other pick which one they want. The player who initiates the pie protocol is termed Slicer and the other player is termed Chooser, though those are just names for convenience, so read the pie rule in question to know how to proceed

Unless specified otherwise, pie protocols result in a game record that is still a legal game without any pie rule (though it may contain bad moves, it won't contain illegal moves). When a player plays a move, they play whichever color is next in the normal sequence of alternation. When a player plays multiple moves, they play whichever colors are next in the normal sequence of alternation. When the pie protocol ends and the game begins, whoever ends up assigned to the color up next in the normal sequence of alternation plays the first move after the pie protocol regardless of who chose who played which side. The pie protocols here follow this norm

AP offers 3 pie rules for Irensei, as well as a default option to play without a pie rule. When the following explanations say a player chooses which color to play, that signals the end of the pie protocol

• Swap-1st (aka Simple Pie)
  1. Slicer plays 1 move
  2. Chooser chooses which color to play
• Swap-2
  1. Slicer plays 3 moves
  2. Chooser chooses one of the following two options
     1. Chooser chooses which color to play
     2. Chooser plays 2 moves
        1. Slicer chooses which color to play
• Swap-5
  1. Chooser starts the game with an “I get to choose colors!” token (hereafter referred to as “the token”)
  2. Loop until 5 moves have been played
     1. Starting with Slicer and alternating between Slicer and Chooser with each iteration of this loop, take one of the following options
        1. Play 1 move and pass the token (if you have it) to the other player
        2. Keep the token and continue to the next iteration of the loop without playing (this option is only available if you already have the token, whether from a previous turn or from just being passed it)
  3. Whoever has the token chooses which color to play

• Choosing a color is done by playing a move (if the interface already shows you as the correct color) or passing (if the interface currently shows you as the incorrect color)
• In Swap-5
  • The option to keep the token and continue the loop is represented by passing
  • The token is not shown anywhere, but inferred from the history of passes

Feel free to add your custom css and/or paintbrush json here

Inspired by Gomoku boards with their 5 star points and using (mostly) the Solarized color palate. The background is 798a89, found by mixing the colors of the White and Black stones in a perceptually uniform color space, OKLAB

/* Remove the gutter shading. */
g#gridlines polygon {
    opacity: 0;
}
 
/* Demarcate the boundary of the central 15×15 region. */
g#gridlines [y1="100"][y2="100"],
g#gridlines [y1="800"][y2="800"],
g#gridlines [x1="100"][x2="100"],
g#gridlines [x1="800"][x2="800"] {
    stroke-width: 3px;
}
 
/* Remove the thick-line extensions into the gutter. */
g#gridlines [y1="100"][y2="100"][x1="0"],
g#gridlines [y1="100"][y2="100"][x1="50"],
g#gridlines [y1="100"][y2="100"][x1="800"],
g#gridlines [y1="100"][y2="100"][x1="850"],
g#gridlines [y1="800"][y2="800"][x1="0"],
g#gridlines [y1="800"][y2="800"][x1="50"],
g#gridlines [y1="800"][y2="800"][x1="800"],
g#gridlines [y1="800"][y2="800"][x1="850"],
g#gridlines [x1="100"][x2="100"][y1="0"],
g#gridlines [x1="100"][x2="100"][y1="50"],
g#gridlines [x1="100"][x2="100"][y1="800"],
g#gridlines [x1="100"][x2="100"][y1="850"],
g#gridlines [x1="800"][x2="800"][y1="0"],
g#gridlines [x1="800"][x2="800"][y1="50"],
g#gridlines [x1="800"][x2="800"][y1="800"],
g#gridlines [x1="800"][x2="800"][y1="850"] {
    stroke-width: 1px;
}
 
/* Enlarge the hoshi. */
g#gridlines circle {
    r: 6px;
}
 
/* Hide the four side hoshi for a Gomoku-style arrangement. */
g#gridlines circle[cx="150"][cy="450"],
g#gridlines circle[cx="450"][cy="750"],
g#gridlines circle[cx="750"][cy="450"],
g#gridlines circle[cx="450"][cy="150"] {
    opacity: 0;
}
 
/* Move the four corner hoshi inward for a Gomoku-style arrangement. */
g#gridlines circle[cx="150"][cy="150"] {
    cx: 250px;
    cy: 250px;
}
 
g#gridlines circle[cx="750"][cy="150"] {
    cx: 650px;
    cy: 250px;
}
 
g#gridlines circle[cx="750"][cy="750"] {
    cx: 650px;
    cy: 650px;
}
 
g#gridlines circle[cx="150"][cy="750"] {
    cx: 250px;
    cy: 650px;
}

{
  "colourContext": {
    "background": "#798a89",
    "board": "#798a89",
    "strokes": "#000",
    "borders": "#268bd2",
    "labels": "#000",
    "annotations": "#cb4b16",
    "fill": "#798a89"
  },
  "palette": [
    "#073642",
    "#eee8d5"
  ],
  "glyphmap": []
}