1

Just plain silly.

Replace all pieces of Black (except the king — you are not Chuck Norris, you must have one) with queens. The starting position is then a Mate in 3 (#3).

Challenge: Replace only a few Black pieces with queens such that Lichess (or your favorite engine) shows a forced mate in n, with n as high as possible. Of course, it is always a forced mate in a higher sense, since already replacing a rook is -7. For the record, I managed a #6.

4
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    The problem with the puzzle is that for any large n you're going to be sitting there a long time waiting for Stockfish. I got a #9 but at depth 35 it hadn't found it yet (the 4 queen sacs probably make it think the line isn't worth looking at.) I feel like I'd have to download a dedicated mate solver to go much higher (and even then, all the queen moves would likely slow it down.)
    – D M
    Feb 23, 2022 at 1:47
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    @DM: Yes, I foresaw this problem (and was reluctant to post the question). Feel free to post the #9 anyway. (>SecretagentMan: Naturally #6 by Black :-) Feb 23, 2022 at 8:28
  • What does "a few" mean in "Replace only a few Black pieces...? Feb 23, 2022 at 20:02
  • @SecretAgentMan: A few (of 14 possible) :-) (Specifically, a7 b7 e7 f7 f8 replaced by Q suffices for a #5. This also would be an interesting question: How many replaced pieces suffice for a forced mate inside some defined horizon? I wasn't able to make 4 work, but see answer - 4 also suffice.) Feb 24, 2022 at 9:05

1 Answer 1

3

Improved set-up:

Stockfish gives this one #-13:

[Title "Mate in 13"]
[FEN "rnbqkbnr/qqppppqq/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1"]

1.d4 Qgxd4 2.e3 Qxd1+ 3.Kxd1 Qc5 4.Nc3 Qd6+ 5.Ke1 Qxc2 6.Nge2 Qbxb2 7.f3 Qcd2+ 8.Bxd2 Qdxd2+ 9.Kf2 Qbxc3 10.h4 Qdxe3+ 11.Kg3 Qg7+ 12.Kh3 Rxh4+ 13.Kxh4 Qeh6#

Original Mate in 9 (multiple lines):

[FEN "rnbqkbnr/pqppqqqp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1"]

1. Nh3 Qbxg2 2. Bxg2 Qxg2 3. Rf1 Qh4 4. d3 Qxf1+ 5. Kxf1 Qxh3+ 6. Ke1 Qxf2+ 7. Kxf2 Qdh4+ 8. Kg1 Qxh2+ 9. Kf1 Qh1#
6
  • How about this line: My stockfish says mate-in-14 (at depth 36): [Variant "From Position"] [FEN "rnbqkbnr/qqppppqq/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1"] 1. e3 Qbxg2 2. Bxg2 Qxg2 3. Nc3 Qxh1 4. Ne2 Q7xh2 5. d4 Qa5+ 6. c3 Q1xg1+ 7. Nxg1 Qxg1+ 8. Kd2 Qxf2+ 9. Qe2 Qxe2+ 10. Kxe2 Rh2+ 11. Kd3 Qf5+ 12. Kc4 Ba6+ 13. Kb3 Qb5+ 14. Ka3 Bb7# Feb 23, 2022 at 16:43
  • I'm not sure if I should edit my answer to switch to the new position or create a new answer. Feb 23, 2022 at 16:46
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    @L.ScottJohnson: Edit, keep the #9 and write the #14 below it, marked "Update". Feb 23, 2022 at 16:47
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    I think the issue is simply that it is White's move. So the engine if providing the best line for White, hence your original position really was a Mate in 9 in the since that the best White can achieve is delaying checkmate by 1 move (vs the mate in 8 lines). Feb 23, 2022 at 17:50
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    Yeah, I've edited that in. Stockfish eventually found that around depth 45. Thanks. Feb 23, 2022 at 18:30

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