The Rules Of Dominoes

Robin Linus has done some truly heroic work showing that verbatim Poker can be done in Bitcoin script as it exists today with no extensions. This is still very much a prototype. Much further along than a prototype Nokitlan is supporting games on Chia, including dominoes (this is built on the Chia gaming work of been doing as the fundamental building block and interoperability substrate). Which got me thinking: What are the best dominoes rules to play on Chia? There are many different dominoes variants, with not that much standardization. The tournaments are a four player version which has a very bridge-like feel and is obviously a complete nonstarter for remote play because it’s just begging for cheating via collusion. For two players there isn’t even a completely standardized set of rules, so that’s my excuse for pondering variants, which I’ll do now.

The double-six set of dominoes is a pretty good start for the medium, because if two players alternate discards that’s 28 turns total max is which is more than ideal but somewhat workable. But there are some things which are problematic:

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There’s a lot of go-fish-like cheating, where a player is required to do something based on information only they can see. Go fish is a terrible game, it has tons of cheating by accident which small children will of course do and then learn that that’s a good thing to do. At the very start of the game a player has to do discard with a double or can use any tile they want out of their hand if they don’t have one. It’s much simpler to just make the double six be the first tile on the board at the beginning of every game.

Passing is only allowed if you don’t have a legal move to play, which is a obviously also a huge cheating problem. This doesn’t come up all that often because usually it’s counterproductive to pass, but adjudicating it after the fact is a disaster, especially in combination with tiles getting pulled from the boneyard later so there’s no way for an outside observer to tell what tiles each person had at each time from later play. It’s much better to simply allow passing at any time. If two passes in a row happen then the hand is over. It wouldn’t be too difficult to implement a rule that a player can’t do a second pass ending the hand if they have a legal move but I suspect that would result in some very cheeseball strategies where one player passes until the other player has very few tiles and then with the greater control of ensuing play easily wins the hand.

Pulling from the boneyard is awkward to implement. Notably the common four player game has no boneyard. All 28 tiles are dealt out at the beginning, 7 each to four players. It does result in some interesting hidden information play, but the lesson from Poker seems to be that when it comes to hidden information less is more, and you want it to stay relevant up until the very end instead of having everything eventually become known and then a straightforward endgame. To that end, and because this is a game mechanic I’ve long wanted to use, I think the best approach is to deal out all tiles at the beginning of the game except for one which is permanently out of play and the players don’t find out until the very end which one it is. Then the game becomes all about guessing what that tile is based on the opponent’s play and there’s lots of room for deceptive play.

There’s some random advantage to the player who gets to go first. That could be counteracted with an amount added to the final pip count like komi in Go but there would need to be some playtesting to figure out what a good value for that would be.

Putting this all together here are the draft rules of Bram’s dominoes. Needs playtesting:

Played with double six dominoes. At the start of the hand a random domino is removed from play, the double six is played out as the start, and the other 26 dominoes are dealt out 13 to each player. The first player to play is selected randomly.

Players alternate putting down a domino which extends one of the two ends of the chain on the board. They must match the number at the end of that chain with the domino they place. A player may alternately pass and must do so if they have no legal placement move.

If a player plays their last tile then they win. If both players pass in a row then their remaining tiles are revealed and which ever one of them has fewer total pips wins (possibly plus komi added to the player who went first).

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