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Here is a new little retrograde chess puzzle. This one is intended to be (genuinely) approachable - so if you've never tried to solve one of these yourself before, give it a shot!

In this game, not a lot has happened so far. Most pawns didn't move and only two pieces were captured up until now.

What was the first of these captures?

final position

(16+14), FEN: Nrbqkb2/pppppppp/1N6/8/8/7P/PPPPPPPR/R1BQKBn1

(To clarify, what I am asking about is the exact capturing move. That is, you'll need to determine both the nature and the exact locations of the two pieces involved.)

Please provide your reasoning in your answer and have fun solving this! :^)

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    $\begingroup$ This one is intended to be (genuinely) approachable - so if you've never tried to solve one of these yourself before, give it a shot! Well done, and thank you! This is the first retrograde chess puzzle on this site that I was able to completely solve myself (and in a reasonable amount of time). $\endgroup$ Commented Apr 14 at 17:08
  • $\begingroup$ @Heinzi Thanks for the feedback! I'm glad to hear the puzzle worked for you :) $\endgroup$ Commented Apr 14 at 21:34

1 Answer 1

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I think the first capture must have been

The black Rook (Nh6xg8, in fact)

Reasoning:

Black could not have made the last move. The knight on g1 could not have moved from f3, because that would have had the white king in check, and no other piece or pawn could have moved.

Similarly:

White could not have made a non-capture move on his last move, because that would leave black with the same impossibility as above.

Therefore:

White's last move must have been a capture, and it must have occurred on either h2, a1, or b6. The black rook and black knight are the only pieces missing, and the black rook could not have reached any of these squares (and obviously there have been no promotions). Therefore the last move was white's capture of black's knight and the first piece captured must have been the black rook

Following up on the clarification of what is asked for:

The first capture was on g8. In particular, Nxg8.

Why?

parity I think. White has definitely made an even number of moves. e.g. both knights are on different colors (only happen after even number of knight moves). h3, and an odd number of Rh1-h2 moves. and an even number of Rb1-a1 moves. So black must have made an odd number of moves. The knight was captured on a black square and the other knight is on a black square, so that is odd number of knight moves. The rook on b1 moved an odd number of times Ra8-b8 and ended up on b8. The only other piece that could have moved was the rook on h8, so an odd number of Rh8-g8, ending up and being captured on g8 by a knight that must have come from h6. QED

Proof game

1. Nf3 Nf6 2. Nd4 Ne4 3. Nf5 Ng5 4. Nh6 Rg8 5. Nxg8 Nh3 6. Nc3 Ng1 7. Nd5 Nc6 8. Nb6 Rb8 9. Na8 Nd4 10. Nh6 Nb3 11. Rb1 Na1 12. Nf5 Nb3 13. Ne3 Na1 14. Nc4 Nb3 15. Ncb6 Na1 16. h3 Nb3 17. Rh2 Na1 18. Rxa1

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    $\begingroup$ This is a good answer to the question as it is written; I think Tim probably intended to ask for the exact capturing move though, because that information is also available in the position. The method of deducing that is anything but approachable though. :-) $\endgroup$ Commented Apr 13 at 18:22
  • $\begingroup$ Thanks for the quick answer Steve :) So far, it is completely correct! But as @Bass correctly pointed out, I actually intended to ask about the exact capturing move. But apparently, my wording was not too clear - I'll edit the question :) $\endgroup$ Commented Apr 13 at 18:27
  • $\begingroup$ @TimSeifert modified $\endgroup$ Commented Apr 13 at 18:49
  • $\begingroup$ Looks good now! That's a very good answer! :) $\endgroup$ Commented Apr 13 at 19:05

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