Answers.Body: <p>No, it isn't possible because, before Stockfish says it is Mate in 8, it views the position from the aspect of the losing side, i.e, the evaluation is the best that can be obtained by the losing side. </p>
  
  <p>In other words, Mate in 8 is what happens if the losing side plays the possibly best defense. If the losing side plays sub-optimally, it could lose faster, but 8 moves is the longest possible postponement of Checkmate</p>
  
Answers.ContentLicense: CC BY-SA 4.0
Answers.CreationDate: 2018-05-27T04:21:47.680Z
Answers.Text: I don't believe this is correct, however it's possible I'm wrong. What if stockfish makes a mistake because it prunes some possible responses that superficially seem worse but in fact lead to a slower checkmate?
Answers.UserDisplayName: Stoud
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Answers.CreationDate: 2018-01-19T09:08:17.633Z
Answers.LastActivityDate: 2018-01-19T09:08:17.633Z
Answers.UserDisplayName: codebro
Body: <p>I know that it is possible for a chess engine to evaluate a position as mate in X moves, when in fact there exist a mate in smaller number of moves. But can the reverse situation happen?</p>
  
  <p>For example the engine evaluated a position as mate in 8 moves, but actually the best possible mate is in 9 moves (or 10 or 13).</p>
  
  <p>To be more concrete the engine is stockfish.</p>
  
Comments.ContentLicense: CC BY-SA 3.0
Comments.CreationDate: 2018-01-19T08:38:10.143Z
Comments.Text: Assuming Y>0, I suppose that would require some mistake in the programmation of the chess engine. Or you feeding it the position un-precisely, like not informing it that castling rights have been lost.
Comments.UserDisplayName: Evargalo
Comments.ContentLicense: CC BY-SA 3.0
Comments.CreationDate: 2018-01-19T08:48:49.710Z
Comments.Text: @Evargalo yes, assuming Y > 0, otherwise you and up with the example I described in the first paragraph. And yes, assuming there is no mistake in the engine (otherwise if you assume possible mistake, you can justify any evaluation)
Comments.UserDisplayName: Salvador Dali
Comments.ContentLicense: CC BY-SA 3.0
Comments.CreationDate: 2018-01-25T15:36:09.310Z
Comments.Text: @SalvadorDali Good question. The 2nd paragraph of phonon resolved it for me, it's funny how engines sometimes work like us :)
Comments.UserDisplayName: user929304
Tags: <engines><stockfish>
Title: Is it possible for stockfish to tell that mate is in X moves, when mate is in X + Y moves?
ThreadText: # Is it possible for stockfish to tell that mate is in X moves, when mate is in X + Y moves?
  
  (Asked by: username_0 on 2018-01-19)
  
  I know that it is possible for a chess engine to evaluate a position as mate in X moves, when in fact there exist a mate in smaller number of moves. But can the reverse situation happen?
  
  For example the engine evaluated a position as mate in 8 moves, but actually the best possible mate is in 9 moves (or 10 or 13).
  
  To be more concrete the engine is stockfish.
  
  **Tags:** engines, stockfish
  
  > **Comments:**
  > **username_1**: Assuming Y>0, I suppose that would require some mistake in the programmation of the chess engine. Or you feeding it the position un-precisely, like not informing it that castling rights have been lost.  
  > **username_0**: @username_1 yes, assuming Y > 0, otherwise you and up with the example I described in the first paragraph. And yes, assuming there is no mistake in the engine (otherwise if you assume possible mistake, you can justify any evaluation)  
  > **username_2**: @SalvadorDali Good question. The 2nd paragraph of phonon resolved it for me, it's funny how engines sometimes work like us :)  
  
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  ## 1 answers
  
  ### Answer by username_3 on 2018-01-19. Score: 2 | Accepted answer
  
  No, it isn't possible because, before Stockfish says it is Mate in 8, it views the position from the aspect of the losing side, i.e, the evaluation is the best that can be obtained by the losing side.
  
  In other words, Mate in 8 is what happens if the losing side plays the possibly best defense. If the losing side plays sub-optimally, it could lose faster, but 8 moves is the longest possible postponement of Checkmate
  
  > **Comments:**
  > **username_4**: I don't believe this is correct, however it's possible I'm wrong. What if stockfish makes a mistake because it prunes some possible responses that superficially seem worse but in fact lead to a slower checkmate?  
  
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