Answers.Body: <p>In case of 16.hxg3, Black plays 16...Qxg3+ when White has only two legal moves:</p>
  
  <ul>
  <li><p>17.Kh1 Rf6 followed by 18...Rh6 is a quick checkmate.</p></li>
  <li><p>17.Qg2 Qxe3+ and after the check is parried Black can already take back his piece with 18...Qxd3 (with already three extra pawns as a reward), or continue the attack with 18...Rf6. He's completely winning in both cases.</p></li>
  </ul>
  
  <p>This exercise is a typical case of a demolition sacrifice: you give your knight on g3 to rip the opponent king of its protective pawns and mount a decisive attack.</p>
  
Answers.ContentLicense: CC BY-SA 3.0
Answers.CreationDate: 2017-11-09T13:29:48.417Z
Answers.LastActivityDate: 2017-11-09T15:11:07.400Z
Answers.LastEditDate: 2017-11-09T15:11:07.400Z
Answers.UserDisplayName: Evargalo
Answers.Body: <p>lichess's puzzles are computer-generated, in the sense that they are selected by an algorithm from positions arising in games between humans. The solution expected is the engine's top choice. In particular, when the engine defends, it picks the best move according to the engine's evaluation.</p>
  
  <p>Thus, in this case, while the most testing move is 16.hxg3, it leads to a worse position (according to the engine's assessment) than 16.Qg2 (assuming best play by both sides), so the engine defends with the latter move instead.</p>
  
  <p>Of course, if this puzzle was given to you by a human, the move given for white would be  16.hxg3, and you would need to show that you found 16...Rf6. But it's not, and the algorithm that generates these puzzles isn't smart enough to differentiate between the best defense, and the most testing response.</p>
  
Answers.ContentLicense: CC BY-SA 3.0
Answers.CreationDate: 2017-11-09T15:44:55.843Z
Answers.LastActivityDate: 2017-11-09T15:44:55.843Z
Answers.UserDisplayName: Ken Wei
Body: <p>I'm a beginner and right now rated 1850  in on lichess training; so I'm a very novice player. I try to solve some training examples, and though sometimes I do not feel convinced by the solution given by the computer, I continue. 
   Here is an example where I felt the solution was absolutely wrong. Below are the pictures</p>
  
  <p><img src="https://i.sstatic.net/qisn8.png" alt="solution"> </p>
  
  <p><img src="https://i.sstatic.net/qEchJ.png" alt="enter image description here"></p>
  
  <p>Why did the computer save the queen rather than killing the knight on g3 with the pawn on h2? </p>
  
  <p>I thought of this step when solving it but thought it was of no use. But the solution given left me wondering. </p>
  
Comments.ContentLicense: CC BY-SA 3.0
Comments.CreationDate: 2017-11-09T06:06:17.460Z
Comments.Text: You forgot the rook lift ...Rf6, winning in all lines. The puzzle is correct.
Comments.UserDisplayName: SmallChess
Comments.ContentLicense: CC BY-SA 3.0
Comments.CreationDate: 2017-11-09T06:27:55.407Z
Comments.Text: Hey here are  my steps i would do  if white. Nxh2 black goes Qxg3 check  white Qg2. This would be a safe move  isnt it correct?
Comments.UserDisplayName: jack wilson
Comments.ContentLicense: CC BY-SA 3.0
Comments.CreationDate: 2017-11-09T10:42:02.323Z
Comments.Text: And after white Qg2 what if black goes Qxe3 check? Followed by Qxd3 or Rf6?
Comments.UserDisplayName: bof
Tags: <online-chess><lichess>
Title: Correctness of the lichess training solution (Puzzle:63063)
ThreadText: # Correctness of the lichess training solution (Puzzle:63063)
  
  (Asked by: username_0 on 2017-11-09)
  
  I'm a beginner and right now rated 1850 in on lichess training; so I'm a very novice player. I try to solve some training examples, and though sometimes I do not feel convinced by the solution given by the computer, I continue.
  Here is an example where I felt the solution was absolutely wrong. Below are the pictures
  
  ![solution](https://i.sstatic.net/qisn8.png)
  
  ![enter image description here](https://i.sstatic.net/qEchJ.png)
  
  Why did the computer save the queen rather than killing the knight on g3 with the pawn on h2?
  
  I thought of this step when solving it but thought it was of no use. But the solution given left me wondering.
  
  **Tags:** online-chess, lichess
  
  > **Comments:**
  > **username_1**: You forgot the rook lift ...Rf6, winning in all lines. The puzzle is correct.  
  > **username_0**: Hey here are  my steps i would do  if white. Nxh2 black goes Qxg3 check  white Qg2. This would be a safe move  isnt it correct?  
  > **username_2**: And after white Qg2 what if black goes Qxe3 check? Followed by Qxd3 or Rf6?  
  
  ---
  
  ## 2 answers
  
  ### Answer by username_3 on 2017-11-09. Score: 7
  
  In case of 16.hxg3, Black plays 16...Qxg3+ when White has only two legal moves:
  
  * 17.Kh1 Rf6 followed by 18...Rh6 is a quick checkmate.
  * 17.Qg2 Qxe3+ and after the check is parried Black can already take back his piece with 18...Qxd3 (with already three extra pawns as a reward), or continue the attack with 18...Rf6. He's completely winning in both cases.
  
  This exercise is a typical case of a demolition sacrifice: you give your knight on g3 to rip the opponent king of its protective pawns and mount a decisive attack.
  
  
  ---
  
  ### Answer by username_4 on 2017-11-09. Score: 4
  
  lichess's puzzles are computer-generated, in the sense that they are selected by an algorithm from positions arising in games between humans. The solution expected is the engine's top choice. In particular, when the engine defends, it picks the best move according to the engine's evaluation.
  
  Thus, in this case, while the most testing move is 16.hxg3, it leads to a worse position (according to the engine's assessment) than 16.Qg2 (assuming best play by both sides), so the engine defends with the latter move instead.
  
  Of course, if this puzzle was given to you by a human, the move given for white would be 16.hxg3, and you would need to show that you found 16...Rf6. But it's not, and the algorithm that generates these puzzles isn't smart enough to differentiate between the best defense, and the most testing response.
  
  
  ---
  
  