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A forced checkmate is a situation in which the player whose turn it is has only legal moves which put the other player in checkmate.

I’m searching for the minimal forced checkmate (the smallest amount of pieces). If there are several with the same amount of pieces, the one with the most legal moves (which all need to checkmate) wins.

A similar question was asked here, but it wasn’t about a minimal position:

A position in which checkmate is forced (obligatory)

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  • Are fairy pieces allowed or do you just want standard chess pieces for the answer? Oct 13, 2022 at 6:00
  • I waun’t interested in fairy pieces, no :-)
    – Alfe
    Oct 13, 2022 at 11:01

1 Answer 1

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Here's a reachable position (white to play) with five pieces and six legal moves, all of which checkmate. This was found with the assistance of computer search and some manual input from me.

[Variant "From Position"]
[FEN "5Q2/7k/4p3/5K2/4B3/8/8/8 w - - 0 1"]
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  • 5 pieces are minimum indeed (unless fairy pieces are allowed, see above, e.g. an amazon Q+N allows 4, and if we get wacky with a berolina pawn king, 2 :-). Material-wise Ka1 Bb1 Rc4 - Ka3 Pb3 should be optimal. Oct 13, 2022 at 7:22

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