It is possible to reach (exactly) #8 after just 3 moves:

[Title "#8 after 3 moves"]
[FEN ""]

1. e3 f6 2. Qf3 Kf7 3. Nh3 Qe8! 4. Ng5+ Kg6 5. Bd3+ Kxg5 6. Qf4+ Kh5 7. g4+ Kh4 8. Qg3+ Kg5 9. f4+ Kh6 10. g5+ fxg5 11. Qxg5#

Is there any longer forced win than #8 that can be reached (and proven) after just 3 moves?

This question is a variant of, and therefore not a duplicate, "The quickest mate in n."

  • 2
    Just two minor comments: For a brute force attack, you have to check about 100 million positions (quickly googled that; with some intelligent guessing you surely can bring that down - 1.e~ is probably forced, and likewise 1...d/e/f~). Second, it would also be remarkable if the resulting position would be correct as a chess problem (e.g. here h4+ works as well as f4+). – Hauke Reddmann May 29 at 19:58

After playing around in Lichess's analysis page, I found a mate in 10. Throwing the moves into chess.com's analysis page provides further confirmation. It has a few wholly unique lines, and some dualed ones, making it reminiscent of a chess problem per @Hauke Reddmann's above comment.

[FEN ""]
[Title "#10 After 3 Moves"]

1. e4 d5 2. h3 Kd7 3. Bb5+ Ke6 4. Qg4+ Kd6 5. e5+ Kc5 6. b4+ Kxb5 7. a4+ Kb6 8. a5+ Kc6 9. b5+ Kc5 10. Ba3+ Kxb5 11. Nc3+ Kc6 12. Qa4+ b5 13. Qxb5#

It can be done the other way around as well.

[Title "#10 After 2.5 Moves"]
[FEN ""]

1. d4 e5 2. Kd2 Bb4+ 3. Ke3 Qg5+ 4. Kd3 e4+ 5. Kc4 b5+ 6. Kxb4 a5+ 7. Kc3 b4+ 8. Kb3 a4+ 9. Kc4 Ba6+ 10. Kxb4 Nc6+ 11. Kc3 Qa5+ 12. b4 Qxb4#
  • 1
    Well, in terms of finding "what is the theoretical perfect line of play for Black after 1. e4 we can strike 2...Kd7 3...Ke6 off that list. – BaseZen May 29 at 22:00
  • Impressive. (I tried out a few other setups on the queenside, but no luck.) – Hauke Reddmann May 30 at 10:28

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