6

Inspired by this position from a game I played.

[FEN "r1b2rk1/p2p1p1p/2qb1PpQ/2p1p3/2p1P3/5N2/PPnP2PP/R1B2RK1 b - - 0 1"]

Black has almost all their pieces, is not in check, and can make 27 (by my count) moves. None of them can prevent mate next turn.

Let's take this further. What legal position has the most possible moves yet results in being mated next move?

1
  • I've blundered this mate pattern. I noticed computers will sometimes preemptively move the rook
    – qwr
    Oct 15, 2023 at 22:55

2 Answers 2

3

I bid 200 moves, with two moves added courtesy of an improvement by @James Martin.

R4Q2/2Q4Q/4Q3/1Q4QB/3Q3b/Q4R1q/2Q1rprN/2nbBKNk w - - 0 1 
9
  • 1
    Very nice!! How about replacing the black pawn on g3 by a black bishop on h4, and then adding a white bishop on h5? I think that gains a couple! Oct 14, 2023 at 18:09
  • @JamesMartin Indeed it gains one, thanks. Just shy of 200... Oct 14, 2023 at 19:45
  • Presumably I'm overlooking something obvious, but why doesn't it gain 2? Newly possible: Be8, Bf7, Bg6, Bg4, Qxg2+, Rxh3. No longer possible: Qgh5, Qhh5, Qhh4, Qhxh3. Oct 15, 2023 at 15:20
  • @JamesMartin You’re right, I miscounted. Needed a fresh look, it seems. Oct 15, 2023 at 20:19
  • 1
    @Allure fxe1=Q#/R#. Oct 15, 2023 at 23:22
2

I only write this as an answer (it isn't) as this is an invaluable source for one-move records, with citations (surely more questions on CSE apply). Since the positions are rather old some records might be broken (or will be broken by Rewan after he fought through the linked site's Excel table).

Sorry, German only

According to the table (if I interpret the terminology correctly) this would be "erzwungene Mattduldungen". You can search this simply in the SCHWALBE PDB by entering this term as STIP= search. Since even "voluntary" instead of "forced" gives only a record of 201 (P1179075) under this side condition ("With promoted material, legal" - seven subtypes are listed), I guess Rewan's record stands. Allowing illegal positions, 255 (P0005619). Forbidding promoted pieces, 135 (P1178928). Since this peculiar record is missing, I suggest Rewan updates the PDB.

(off to alert MatPlusForum)

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