A complete game of Lifeline.
Lifeline is a territorial strategy game for two players (Black and White) that is played on the cells of a hexhex board. Base 6 is the smallest recommended size. The game was invented by Michael Amundsen and Luis Bolaños Mures.

Definitions

A group is an entire set of connected stones of the same color. A single stone, not connected to others of its color, is also a group.

A group is dead if there is no path of connected empty cells between that group and any other of its color.

Setup

Starting with Black, the players take turns placing stones of their own color on empty cells, one stone per turn.

The setup ends when each player has two stones on the board. These two stones must not be adjacent to each other.

Play

After the setup, the players continue taking turns in the same order. On your turn, perform the following actions in the stated order:

1. Place a stone of your color on an empty cell.
2. Remove all dead enemy groups.
3. Remove all dead friendly groups.

The board positions at the start and at the end of your turn must be different.

The last player to make a placement wins. Note that you will always have a placement available unless your turn starts with no groups of your color on the board.

The rules look mostly ok, unless forced cycles can occur but, at first glance, seem unlikely. Have you tried the game and is it interesting in practice?

Cycles are impossible, thankfully. And yes, it is very interesting in practice Some people are playing it in the iggc sandbox. That's the place to check it out if you want to try it. The game will also be in the next release of Ludii.

There are no cycles, forced or otherwise. The game is fully drawless.

A few abstract game enthusiasts have tried the game on the igGameCenter sandbox. Feedback has been positive so far. Life and death fights are often quite brutal, and, overall, the game feels very different from Go.

We have also found three different types of seki (never mind the tiny boards in these diagrams):



In the first one, a placement by either player on either empty cell is suicide. In the second one, both players can capture an enemy group by playing on either empty cell, but neither player wants to do so. In the third one, a placement by Black on either empty cell is suicide, and White can capture two black groups by placing on either empty cell, but does not want to.

"A group is said to be cornered if it reaches one or more enemy groups and no friendly groups."

Black plays the first move. But then when White plays, aren't both black and white cornered? There is a single black group and a single white group. They reach each other. So they both reach one enemy group, and neither reaches a friendly group? So then White captures black. Then black plays a single stone and captures white? etc etc?

Why can there be no cycles?

Note that, at the start of the game, there is a setup phase with no capture rule. At the end of the setup, there will be two groups of each color on the board.

When you capture an enemy group, you create an empty region that reaches no groups of your opponent's color. This means your opponent can make no further placements in that region.

Ah, ok, that is because of the move rule "On your turn, place a stone of your color on any cell in an empty region that is adjacent to one of your groups".

We have updated the rules to allow suicide, as we learned that suicide can be useful in the endgame. The game is now simpler and deeper (slightly so).

My original post now shows the updated rules.