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This is chess between three players. Short rules:

  • Black moves first, then blue, then red. The move order is the same regardless of whether any of the players are in check.
  • Normal chess rules regarding piece movement, capture and checkmate apply.
  • Black pawns move upwards, blue and red pawns move downwards.
  • If one player gets checkmated when the other two players are still in play, the checkmated player is out of the game but their pieces remain on board. These pieces cannot move or make captures, but they can still be captured by the other players' pieces. A checkmated king can be captured like any other piece.
  • All players play their best moves, so no collaboration or softplay.

Black to move and checkmate both opponents in the smallest number of moves possible.

enter image description here

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    $\begingroup$ Inspired by Chess Golf: Peaceful Double Mate. $\endgroup$
    – Jafe
    Aug 28, 2019 at 12:26
  • $\begingroup$ good one I think the game like this can be made in real we just need bigger board and it will be fun... $\endgroup$ Aug 28, 2019 at 12:38
  • $\begingroup$ @SayedMohdAli There are some existing chess variants with three players, but I think they're usually played on some kind of weirdly shaped board :) $\endgroup$
    – Jafe
    Aug 28, 2019 at 12:42
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    $\begingroup$ @StephenTG Out of the game. I'll add a mention of this in the rules. $\endgroup$
    – Jafe
    Aug 28, 2019 at 14:38
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    $\begingroup$ You did get the intended answer, but blue's best move actually is collaboration. Nd5 or such leaves red with Kg6. Sure, blue can be checkmated in one by black's Nd6, but blue knows that black won't play it as he would lose queen (and game) to red. Simple solution = change move order and have red go after black. Red would play Qe7; but after black's Nd6 he gets checkmated anyway. This time, it is NOT in blue's interest to collaborate and move knight, as black can still play Nd6, winning against blue and not losing against red (material is the same; unless blue took one pawn with knight) $\endgroup$ Dec 5, 2023 at 14:19

3 Answers 3

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I think the best I can do is 4 moves.

1.Qd7+, c5#, Red is now dead, don't worry about him anymore
2.Nxc5+, Ka7
3.Ne4+, Kb7 or Qb6
4.Nd6# or Qxc7#

Another mentioned variant

1.Qd7+, Qb6, Qe7
2.Nd6#, Ka7
3.QxC7#

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  • $\begingroup$ The gist of this is correct. However, I now realize that this turned out more complicated than intended because of lines like 1.Qd6+ Qxb4# which allow blue to make some spite checks to delay mate. That was an oversight on my part. $\endgroup$
    – Jafe
    Aug 28, 2019 at 17:55
  • $\begingroup$ @jafe you are right that is my 5 moves solution is best because he will try to delay the game as much as he can because in a game of chess the clock keeps on ticking... $\endgroup$ Aug 29, 2019 at 5:48
  • $\begingroup$ I think it's actually a mate in 8 if blue plays 1...Qxb4#. (Which means it's also blue's best move, because 1...c5# leads to a mate in 4 as above and every other move allows Nd6# on the next move.) $\endgroup$
    – Jafe
    Aug 29, 2019 at 6:22
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Here is the shortest solution...

best 5 move solution with explanation.

1 -> d6- d7 - so this move will easily mate the red king now he is out of the game and so his pieces. because of the blue knight blocking g6... now blue is having turn so his best move will be...I am not getting any good move in his end I assume that he is a good chess player and he already knew that my next move will be e4 - d6 to mate him. so his best move to defend is a5-b6 he can sacrifice his queen to safe the check-mate of the next move. I will give a check to him with my knight

2 -> e4-c5 he has no choice but to move his king to a7 now I will move my

3 -> knight to e6 so he knows that I am coming after his bishop with my knight and queen to he will bring his king back to b7 to support. now i will take down his

4-> queen with my bishop b6

5-> and finally queen to c7 to mate the blue king

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    $\begingroup$ red moving Qe7 would still be checkmated by black's second move of Nd6. However, I think Blue's move to survive the two move checkmate should be pawn to c5, which would incidentally block rQe7. $\endgroup$
    – Sconibulus
    Aug 28, 2019 at 14:15
  • $\begingroup$ @Sconibulus Yes, you're right or Blue could do Qb6 followed by Ka7 $\endgroup$
    – hexomino
    Aug 28, 2019 at 14:30
  • $\begingroup$ @Sconibulus yes, i did not read everyone will play their best move. but with the best moves of the blue he will get mated in 5 moves... as explained... $\endgroup$ Aug 28, 2019 at 14:54
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The problem is that best play may be collaboration.

After black moves Qd7, blue's best move is collaboration. Nd5 leaves red with move Kg6. Black has a dilemma - move Nd6 checkmates blue. But after red's Rxd7, it is red that is totally winning. So, black cannot play Nd6 to win against blue as it would be a game-losing move. He actually doesn't have ANY good move, the queen is gone whatever he does. Therefore, black wouldn't play Qd7 knowing it is a losing move.

What would he play?

Nc5 Ka7 ... allows red to help blue by Ne3+ and black loses ... so this another nice aggressive plan is once again not in his best interest. What about Qc5? Queen is safe enough, this position seems a deadlock as nobody wants to exchange material (the third player would come out the best), there are no reasonable threats etc ...

Now, what if move order is changed a bit to black, red, blue? This allows a solution.

Qd7 Qe7 ???; Nd6. This move would checkmate red and blue if blue doesn't move anything. First let's check what if he tries moving knight again - missing move is Nd5 (or similar). Red moves Kg6, blue is checkmated and black has 2 viable moves: Qxe7 and Qxc6. Both of these leave black and red with equal material, I would guess black has a slight positional advantage that could let him at least draw if not win, making the Qd7+Nd6 still in his interest. So, as blue plays optimally, his missing move is NOT moving knight but trying to survive for as long as possible.

So, we have the final solution to the revised problem:

(black, red, blue)

(I am clueless how to make this move order to a sane line-by-line spoiler so it is unspoilered. Sorry.)

  1. Qd7 Qe7 Qb4;
  2. Nd6 ### Qxd6;
  3. Rxd6 ... Ra1;
  4. Be1 ... Rxe1;
  5. Kxe1 ... Nxg2;
  6. Kd2 ... c5;
  7. Qc5 ... Ka7;
  8. Qxa6#
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