Why can the bishop just take the knight in this Lichess puzzle?

Question

In this Lichess puzzle, after the initial moves

[title "Black to move"]
[fen ""]
[Startply "17"]
[StartFlipped "1"]

c4 b5 2. cxb5 Bb7 3. Nf3 g5 4. Nxg5 Bg7 5. Nf3 c5 6. Nc3 a6 7. d4 axb5 8. Nxb5 Qa5+ 9. Nc3 Bxf3!

Why can the bishop just take the knight? Why is it so bad for white to retake on f3?

If white takes bishop, theb b cxd4 and taking the knight next move — Arctic Char, Mar 04 '22 at 12:16
The meaning of my question seems to have got lost during editing (now restored). I didn't want to give the puzzle away, but I was apparently not clear enough initially. — hkBst, Mar 04 '22 at 15:29
@cmgchess, you would think that taking back the bishop was a no-brainer, but the computer thinks it is very bad to do that (with either pawn). The computer thinks the solution is to take the knight and then for white to play Bd2, and then black can move its bishop away. If you take on f3 then the eval goes down more than 3 points! — hkBst, Mar 04 '22 at 15:37
@hkBst i mean even if he didnt take back and played Bd2 he'll be down a piece for no compensation after black retreats the bishop. — cmgchess, Mar 04 '22 at 15:48
The bishop CAN take the knight because the bishop is directly attacking the knight. It's a perfectly valid and legal move. I think you probably meant to ask Why SHOULD the bishop take the knight? — JK., Mar 06 '22 at 06:03
@JK. not "can take", but "can just take", as in "without any consequences" or "as if the knight is hanging". I think that is correctly implied, and different from "should take". — hkBst, Mar 06 '22 at 15:00

Brian Towers · Accepted Answer · 2022-03-06T23:08:11.350

10

Here's why:

[FEN "rn2k1nr/1b1pppbp/8/q1p5/3P4/2N2N2/PP2PPPP/R1BQKB1R b KQkq - 1 1"]
1...Bxf3 2. exf3 cxd4 3. Bd2 (3. Qxd4 Bxd4) dxc3 4. bxc3 Bxc3 5. Rc1 Bxd2+ 6. Qxd2 Qxd2+ 7. Kxd2 Rxa2+ 8.Ke3 Nc6

White is completely lost.

edited Mar 06 '22 at 23:08

answered Mar 04 '22 at 16:41

Brian Towers

96,800
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True. I can relate to the OP's confusion though: lichess puzzles are often the most puzzling in where they stop and consider it done - sometimes you would just play the move that feels right and it says "congratulations, you won!" all while you sit there stumped. – Lodinn Mar 04 '22 at 20:16
4

@Lodinn: For those of us with lower ratings, there's also the problem that in our practical experience, a "good" move is a move which is not a blunder, rather than an actual good move. – Kevin Mar 04 '22 at 20:41
5

@Lodinn sometimes it feels like it's saying "yes you get the idea, no need to make you play out the rest of the obvious moves" which in my experience is correct maybe 50% of the time – llama Mar 04 '22 at 23:07
6

@llama I think that more often, it's really saying "Yes, now there's a few ways to win from here, but we have a strict requirement that there is exactly one correct solution to our puzzles so the puzzle must end here" – Edward Mar 05 '22 at 04:36
2

Subtract one point for not taking a2 with check before Nc6 :-) – Hauke Reddmann Mar 05 '22 at 08:38
@HaukeReddmann wait, what? – Michael Mar 06 '22 at 22:42
@Michael: That was a joke referring to the playing style of computers (and consequently, the sometimes strange way such puzzles are evaluated). At the end of Brian's variant, Nc6 (or something else, but Nc6 is obvious and best) is absolutely needed to stop White from Rc8#. But since taking the pawn is more gratis material, and the check hinders Rc8# for a move, a computer would complain about immediate Nc6. – Hauke Reddmann Mar 07 '22 at 07:32

score 8 · Answer 2 · answered Mar 04 '22 at 16:26

8

After retaking the bishop, Black will take on d4 with his pawn, attacking the pinned knight. White can do nothing to stop Black from capturing it "for free" on the next move.

answered Mar 04 '22 at 16:26

David

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score 7 · Answer 3 · edited Mar 07 '22 at 02:44

After you complete the puzzle, " Stockfish 14+NNUE in local browser" appears in the upper right (just above the list of moves), and a toggle button appears to the right of that. If you click it, it will suggest the continuation 10. Bd2, but you can play around with other lines by making those moves on the board. For instance, after 10. gxf3, the engine recommends 10. ... cxd4. As it has been captured, the knight is not available to capture the pawn, and the queen is deterred by the bishop on g7. As the knight is pinned, it can't be moved away.

Why can the bishop just take the knight in this Lichess puzzle?

3 Answers3