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You are in a regular chess tournament, your opponent is Deepest Blue AI who considers every kind of possibilities and does not make any mistakes.

But you are given an opportunity to remove any pieces of your opponent's but you cannot remove any piece from yours.

What is the least amount of pieces to be removed to guarantee to win the game with the least amount of moves?

Note that Deepest Blue AI wants to take the game as long as possible. It is also your turn to start.

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    $\begingroup$ Removing the king would do it in zero... ;-D $\endgroup$ – Konchog Jan 10 at 12:09
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    $\begingroup$ So you remove as many as you want at the beginning and then play. If you remove p pieces and mate in m moves what are we trying to optimize? Is it minimum m with smallest p? Or m+p? Or minimum p with smallest m? $\endgroup$ – Dr Xorile Jan 10 at 14:17
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    $\begingroup$ @DrXorile thats very good question, my intention is to find least moves with the most pieces, so if we accept @glorfindel’s answer, the actual answer i am looking for is more pieces with at most 6 moves. i hope it is clear now. $\endgroup$ – Oray Jan 10 at 16:32
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Just to give a baseline answer:

if you remove all Black's pieces except the king, it's mate in 6. E.g. 1. e4 Kd7 2. Qg4+ Kd6 3. Qg7 Kc6 4. d4 Kd6 5. Bf4+ Ke6 6. d5# (or 2... Ke7 3. Qg7+ Kd6 4. d4 Kc6 5. Bf4 Kb6 6. Qc7#, or 2... Kd8 3. Qg7 Kc8 4. Bb5 Kb8 5. Ba6 Ka8 6. Qb7#).

It's certainly possible that

there is a solution where Black still has a pawn or other piece which doesn't help avoiding mate any longer.

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  • $\begingroup$ Why does the black king retreat to the 8th rank in the 2nd move? I'd assume it could survive longer by advancing to the 6th rank or staying at the 7th. $\endgroup$ – Sleafar Jan 10 at 9:03
  • $\begingroup$ Good question, but it doesn't seem to matter; I've added some alternative lines. $\endgroup$ – Glorfindel Jan 10 at 9:26
  • $\begingroup$ Here is a lichess link with the position you mentioned. You can turn on local evaluation to let Stockfish calculate the number of moves to mate. There are probably so many possible variants, that posting some of them here will only scratch the surface. It's funny that adding a black pawn on e7 already doubles the number of moves needed to mate the black king. Maybe you already found the optimal solution. $\endgroup$ – Sleafar Jan 10 at 14:18
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    $\begingroup$ And I have a forced mate in 24 with no pieces removed. ;-) $\endgroup$ – Dr Xorile Jan 10 at 14:18
  • $\begingroup$ @DrXorile Too bad you have to wait till 2020 to challenge Carlsen. ;) $\endgroup$ – Sleafar Jan 10 at 14:21
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I believe the answer is:

One piece (the king), in six moves, which reiterates Glorfindel's answer.

This was tested using the Stockfish.js 10 Engine on Chess.com. Most of these were tested up to 40+ depth.

Here are a few setups I tested (mate in x moves denoted by "+Mx"):

> One piece: (best: mate in 6)
Ke8: +M6 1.e4 Kf7 2.Qg4 Kf6 3.Qd7 Kg6 4.d4 Kf6 5.Bc4 Kg6 6.Qf7#

> Two pieces: (best: mate in 7)
Ke8, a7: +M7 1.e4 Kd7 2.Qg4+ Kd6 3.Qg7 Kc6 4.Nc3 a6 5.Nd5 Kd6 6.Qc7+ Ke6 7.Qe7#
Ke8, b7: +M7 1.e4 b5 2.Bxb5+ Kd8 3.Qf3 Kc7 4.Qf6 Kb7 5.Qd8 Ka7 6.Qc7+ Ka8 7.Bc6#
Ke8, c7: +M7 1.e4 Kf8 2.Qg4 Ke7 3.d4 c6 4.Qc8 Kf6 5.Bc4 Kg6 6.Qg4+ Kh7 7.Qg8#
Ke8, d7: +M7 1.e4 d5 2.Qg4 Ke7 3.Qg7+ Kd6 4.exd5 Kxd5 5.Qg6 Kc5 6.Nc3 Kd4 7.Qd6#
Ke8, e7: +M7 1.e4 Kd7 2.Qg4+ Kd6 3.Nc3 e6 4.Qg7 Kc6 5.Nb5 Kb6 6.Qc7+ Ka6 7.Qa7#
Ke8, f7: +M7 1.e4 Kf8 2.Qh5 Ke7 3.d4 Ke8 4.Bc4 Kd7 5.Qxf7+ Kc6 6.Bf4 Kb6 7.Qc7#
Ke8, g7: +M7 1.e4 Ke7 2.Qg4 g5 3.Qxg5+ Kf7 4.e5 Kf8 5.Bb5 Kf7 6.Qh6 Ke7 7.Qf6#
Ke8, h7: +M7 1.e4 h6 2.Qh5+ Ke7 3.Qxh6 Kd7 4.Bb5+ Kc7 5.Qc6+ Kb8 6.Ba6 Ka7 7.Qb7#
Ke8, Bf8: +M8 1.e3 Ke7 2.Qg4 Bh6 3.Bb5 Kf7 4.b3 Bg7 5.Qf5+ Bf6 6.Bb2 Kg8 7.Qxf6 Kh7 8.Qg7#
Ke8, Nb8: +M9 1.e3 Ke7 2.Nc3 Nc6 3.Nd5+ Kd6 4.Qf3 Ne5 5.Qf6+ Kxd5 6.e4+ Kxe4 7.Qe6 Kd4 8.c3+ Kc5 9.b4#
Ke8, Ng8: +M9 1.e3 Nf6 2.Bb5+ Kf8 3.Qf3 Kf7 4.b3 Ke7 5.Bb2 Nd7 6.Qf5 Kd6 7.Qxd7+ Kc5 8.Qc6+ Kb4 9.Bc3#
Ke8, Bc8: +M10 1.d3 Be6 2.Qd2 Kd7 3.Qh6 Bd5 4.Nc3 Bc6 5.Nf3 Kc7 6.Nd4 Ba8 7.Ndb5+ Kc8 8.Qg7 Kd8 9.Bg5+ Kc8 10.Qc7#

> Three pieces: (best: mate in 7)
Ke8, a7, h7: +M7 1.e4 Kf8 2.Qh5 h6 3.Qe5 Kf7 4.Bc4+ Kg6 5.Qf5+ Kg7 6.Qf7+ Kh8 7.Qg8#
Ke8, a7, e7: +M8 1.Nf3 Kd7 2.Ne5+ Kd6 3.d4 a5 4.e3 Kc7 5.Qf3 Kb6 6.Qc6+ Ka7 7.Ba6 a4 8.Qb7#
Ke8, d7, e7: +M8 1.e3 Kf7 2.Qf3+ Ke6 3.Qf4 Kd5 4.Nc3+ Kc6 5.Qb8 d6 6.Bb5+ Kc5 7.Qc7+ Kb4 8.a3#
Ke8, Bg8, h7: +M9 1.e3 g6 2.Qg4 Ke7 3.Qxg6 Kd7 4.Bb5+ Ke7 5.Nc3 Kd8 6.Nd5 Kc8 7.Qe8+ Kb7 8.Bc6+ Ka7 9.Qa8#

> Four pieces: (best: mate in 8)
Ke8, a7, b7, h7: +M8 1.e4 Kd7 2.Nc3 a6 3.Qf3 Kc7 4.Nd5+ Kb8 5.Bxa6 bxa6 6.Qf7 Ka8 7.Qc7 h6 8.Nb6#
Ke8, a7, g7, h7: +M8 1.b3 g5 2.e3 Kf7 3.Qf3+ Ke6 4.Bc4+ Ke7 5.Ba3+ Kd8 6.Ba6 Kc7 7.Qb7+ Kd8 8.Qe7#
Ke8, Bf8, e7, g7: +M9 1.e4 e5 2.Qh5+ g6 3.Qxg6+ Kd8 4.Bb5 Ke7 5.Nf3 Kd8 6.Qe8+ Kc7 7.Qc6+ Kb8 8.Ba6 Ba3 9.Qb7#

> Five pieces: (best: mate in 8)
Ke8, a7, b7, g7, h7: +M8 1.e4 a6 2.Qh5+ Kf8 3.Bc4 Ke7 4.Qf7+ Kd6 5.Qxb7 Kc5 6.d4+ Kxc4 7.Qc6+ Kxd4 8.Nf3#
Ke8, Bf8, e7, f7, g7: +M10 1.e3 e5 2.Bb5+ Ke7 3.Qh5 g5 4.Nf3 e4 5.Qxg5+ f6 6.Qf5 Kd6 7.Qxf6+ Kc7 8.Qc6+ Kb8 9.Ba6 exf3 10.Qb7#

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If you remove a pawn you can kill the king in three moves with the bishop, you need one move to move a pawn, one move to position the bishop and one to kill the king.

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    $\begingroup$ You should probably further explain the moves (i.e. where the specific pieces go) $\endgroup$ – eye_am_groot Jan 10 at 16:06
  • $\begingroup$ I dont understand the stupid chess notation $\endgroup$ – Harry Stylesheet Jan 10 at 16:07
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    $\begingroup$ Consider including a picture diagram of the moves instead then $\endgroup$ – eye_am_groot Jan 10 at 16:13
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    $\begingroup$ It sounds like if you only remove one pawn that they will still have plenty of other pieces to thwart your plans. I'm interested in seeing your solution but do note it has to be guaranteed to win the game in that many moves. $\endgroup$ – Chris Jan 10 at 17:14

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