Life In 19x19

Keil (featured in the Abstract Games magazine) is a Go-like game for two players: Black and White. It is played on the intersections (points) of an initially empty hexagonal grid of triangles. Each player must have access to a sufficient number of stones of their own color.

Keil preserves crosscuts and ko thanks to the idea of linking points, which reduces the natural connectivity of the board. Otherwise, the rules are the same as in Go.

Definitions

Two adjacent same-color stones, or a stone and an adjacent empty point, are linked if there is another point adjacent to both that is not occupied by the other color. Two adjacent empty points, on the other hand, are always linked.

A group is a stone together with all other stones one could reach from it through a series of steps between linked stones. Since only same-color stones are linked, all stones in a group are the same color.

A liberty of a group is an empty point linked to at least one stone in that group.

Similarly, a territory is an empty point together with all other empty points one could reach from it through a series of steps between linked empty points. You own a territory if all stones linked to points in that territory are of your color.

Play

Black plays first, then turns alternate. On your turn, you must pass or place a stone of your color on an empty point. After a placement, remove all enemy stones in groups without liberties. After all removals, the stone you placed must be part of a group with at least one liberty, and the current board position must be different from the board positions at the end of all your previous turns. Otherwise, your placement is illegal.

The game ends when both players pass in succession. The player with the higher score in the final position wins. A player's score is the number of stones of their color on the board, plus the number of points in their territories, plus a komi in the case of White.

Komi and button

The komi is the number of points which is added to White's score at the end of the game as a compensation for playing second. Before the game starts, the first player chooses the value of komi, and then the second player chooses sides. Alternatively, both players may just agree on a value. To avoid ties, it is suggested to either set komi to half a point higher than a whole number (like 6.5) or to use a whole value along with the button.

The button is a special token which is placed next to the board at the start of the game. On your turn, if neither player has taken the button yet, you may not pass, but you may take the button instead of making a board play. At the end of the game, a half point is added to the score of the player who has taken the button. When checking for repetitions, two otherwise identical positions are considered different if the button had already been taken in one of them but not in the other.

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Edit summary: Rules text thoroughly reworked for clarity, without changing the game. Added section on komi.

(Note: The following diagrams feature hexagonal grids with play on the spaces rather than triangular grids with play on the intersections. Both options are of course equivalent.)

A crosscut looks like this:



And here are some ko shapes:




In all cases, Black can start the ko by playing at 1 and removing the marked white stone.

These are the smallest living shapes in the corner:



This is the smallest living shape in the edge of the board:



And here is the smallest living shape in the middle of the board:

Huh, this looks pretty neat! It's interesting that living shapes can be so chunky and fat, haha. Might be cool to play a few games of this some time.

Applebaps wrote:It's interesting that living shapes can be so chunky and fat

Indeed, that's because two adjacent stones are not permanently connected until there is a third, same-color stone adjacent to both.

Here is a picture of a finished game for good measure. Black won by 0.5, with 67 points to White's 66.5. Komi was 6.5 points. In this case, stones were placed on the intersections of a hexagonal grid of triangles instead of the spaces of a hexhex grid. The small stones are territory points:

The picture in my previous post was taken from this game:



Thoughts?

I've thoroughly reworked the rules text in my original post for clarity, without changing the game. Feedback on the previous version indicated the concept of domain was confusing and artificial. The new text uses the familiar terms of group, liberty and territory instead and provides a clearer definition of "linking" (previously "coupling") as well.

How many variants of Go do you intend to create?

Javaness2 wrote:How many variants of Go do you intend to create?

All of them? (Just kidding.)

My purpose with Keil was not to make just another Go variant, but to solve the over-connectivity problem in hexhex Go.

I'm happy to announce that the latest issue of the revered Abstract Games magazine features an article on Keil written by Lear Bahack.

Keil is now playable, turn-based, on MindSports. There is also an interactive board where you can familiarize yourself with the rules.

If someone wants to give it a try, I'll be happy to arrange a game.