Poker chess: heads-up
Lab · experiment 1 · rules v0.3
The rules in 30 seconds
- Normal chess, but each side has three pieces face down. You see yours, not your opponent’s. A face-down piece can be anything but the king – even three queens.
- A face-down piece moves like the real one. From the way it moves, your opponent works out what it is.
- Each player has 100 chips. Before your move you can bet chips on this game. Your opponent either matches or gives up – and loses everything already put in.
- A game ends with mate, a surrender or a material count after move 30: whoever has more material takes the chips at stake.
- The goal is not to win one game but to win chips over a series. Sometimes it pays to give up at once rather than play a bad deal.
There are two modes, for chips and without chips – the switch is under the title. Play your first game without chips: that is the default on a first visit. The full rules and the poker connection are below the board.
Table
Advanced: ranges in per cent
A bit measures uncertainty. 1 bit is a coin toss; each further bit doubles the options: three face-down pieces start at 7 bits – 125 equal placements. 0 bits – your opponent knows everything.
Moves and bets
New heads-up
What comes from poker
For poker players: each side is dealt pocket pieces, there is a betting round before the first move, like preflop, then you can bet on any turn, a fold gives up the hand, and with no fold and no mate a showdown on material decides. Your opponent’s moves and bets are how you read their range. The buttons: call – match, raise – bet more, fold – give up, blind – the forced entry, pot – the chips at stake.
| Poker | Poker chess |
|---|---|
| The deck | A draw: five ranks at 20% each, repeats allowed |
| Hole cards | Pocket pieces, face down |
| Heads-up | One against one, for chips |
| Blinds | White posts the big blind of 2, Black the small blind of 1 |
| Preflop | Betting before the first move; Black answers the blind first |
| Streets | Every turn: bet or check |
| Fold | Conceding the hand |
| Showdown | The larger material wins; mate wins early |
| Range | Odds for each face-down piece, updated by the moves |
| Equity | The chance to win the showdown on material against the range |
The deal
- A normal board and pieces; a classical start or Fischer 960.
- A draw picks 3, 4 or 5 squares on each side’s first and second rank, never the king’s.
- Each face-down piece is drawn on its own: queen, rook, bishop, knight or pawn, 20% each. Repeats happen: one side may get three queens, the other three pawns. The open pieces stand as in the classical set-up.
- Your opponent only knows where the face-down pieces are. What they are, he reads from your moves and bets.
- A pawn on the first rank moves one square only; the double step belongs to an unmoved pawn on the second rank.
- A face-down piece moves by the rules of its real type and stays face down. Your opponent sees the move and crosses out the types that cannot make it: a step forward fits pawn, rook and queen, a diagonal capture forward fits pawn, bishop and queen, an L-shaped jump gives the knight away.
- A captured face-down piece is turned over. A face-down pawn on the last rank becomes an open queen. Castling works with a rook on the first rank and reveals a face-down rook.
- The arbiter knows everything: it announces check and refuses illegal moves.
Betting: heads-up
- This is heads-up: two players with 100 chips each. Before each hand White posts the big blind of 2 and Black the small blind of 1.
- Preflop comes before the first move, when you see only your own pieces. Black answers first: complete the blind, raise or fold. If Black just completes, White has the option to raise before the first move.
- After that you bet at the start of your turn. You can bet, or just move – that is a check.
- Your opponent calls, raises or folds. A fold concedes the hand: the pot goes to the bettor. At most four bets and raises per turn.
- Pot limit: a bet is at most the pot, a raise at most the pot after the call, the minimum is 2.
- A hand ends with a fold, a mate (the pot to the winner), a stalemate (split) or a showdown after the move set in the options: the pieces are turned over and the larger material takes the pot – queen 9, rook 5, bishop and knight 3, pawn 1.
- Chips carry over from hand to hand and the colours alternate – and so do the blinds. The heads-up ends when one player is out of chips. The score is kept twice: chips won in pots, and hands won and lost.
The computer
The computer cannot see your face-down pieces. To move, it runs through the placements consistent with your moves and looks for the best move in each. To bet, it estimates its chance to win over 40 such placements: it bets strong deals, sometimes bluffs weak ones and calls when its chance beats the price. It does not read your bets – that is its main weakness.
Playing a person
Choose “A person – by link” and create a table: you get a link to send to your opponent. The hand starts when they open it; moves and bets arrive live. Chips carry over from hand to hand, colours alternate, and a table lives for a week after its last move. The server holds the deal: it draws the pieces, checks every move and bet and decides who won. The other side’s face-down pieces never reach your browser until the hand is over, so they cannot be read in the code.
Against the computer everything runs in your browser; games are not saved anywhere. The rules will change until the idea settles.