Puzzle: Forced game end in at most two halfmoves

Question

Compose a position where

It's White to move
White can deliver checkmate or stalemate in 1 move
Or if they make a different move, then Black can deliver checkmate or stalemate in one 1 move

I needed 6 white pieces and 11 black pieces. Beat me!

Toned down example for understanding:

[FEN "7k/7P/7K/6BP/8/8/8/8 w - - 0 0"]

After the next White move, Black is either mated or stalemated, depending on if White plays Bf6 or not. (This does not meet the 3rd requirement).

How is white getting stalemated or checkmated possible in your above example? Plus, black can't even move if white plays Bf6#. But in your condition, it says Latest after Black's answer it's game over. — Abhyuday Vaish, Apr 9, 2022 at 14:15
@AbhyudayVaish: "Toned down example" - with only two possible outcomes. NO example for the wanted position! — Hauke Reddmann, Apr 10, 2022 at 6:51

Brian Towers · Accepted Answer · 2022-04-13 16:01:25Z

2

Just one piece fewer, but how about:

[FEN "5brr/4p1pq/4P1pk/4N1p1/6P1/6PK/6PP/8 w - - 0 1"]

1.Nd7= {Black stalemated} (1.Nf7#) (1.Nxg6 Kxg6#) (1.Nxg6 Qxg6= {White stalemated})

Brian Towers♦

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answered Apr 9, 2022 at 18:51

James Martin

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3

Valid! (1.N~=, 1.Nf7#, 1.Nxg6 Kxg6#, 1.Nxg6 Qxg6=)
– Hauke Reddmann
Apr 10, 2022 at 6:55
Accepted for now, although maybe it still can be economized. E.g. consider the far lighter Kh3 Qb4 Pg2 - Kh5 Ph6 Pg6 Pg5 Ph4 Pg3. Almost! (Qg4#, Qa5=, Qxh4 gxh4=, Qa6 g4#, but after Qf4 Black can choose g4+, game over in 1.5 instead of 1. Too bad!)
– Hauke Reddmann
Apr 11, 2022 at 7:31
Can an acceptance be withdrawn? This still seems early days for this challenge
– Laska
Apr 12, 2022 at 8:19
2

@Laska The OP can always change their mind about accepted answer
– Brian Towers ♦
Apr 13, 2022 at 16:02

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Hauke Reddmann · Accepted Answer · 2022-04-11 09:21:08Z

2

I knew it! 13 pieces:

[FEN "8/6p1/6P1/6PB/6P1/4p1pQ/4Pp1p/5K1k w - - 0 0"]

1.Qg2#/1.Qxg3=/1.Qh4 g2#/1.Qxh2+ K,gxh2=

Note that 5 pieces just stand around against 1.Qg4, which also ends the game, but in 1.5 moves - still too bad!

answered Apr 11, 2022 at 9:21

Hauke Reddmann

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Note: If you drop the "any move ends..." condition, it is possible with a mere 5 pieces: yacpdb.org/#407710
– Hauke Reddmann
Apr 11, 2022 at 10:03
I like it! Nice that white has just four options, each of which leads to a different outcome.
– James Martin
Apr 11, 2022 at 10:52
@DialFrost: BTW, your deleted solution is perfectly legit, if only a bit illegal. :-)
– Hauke Reddmann
Apr 11, 2022 at 17:49

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2 Answers 2