Answers.Body: <p>This variant is distinct from regular chess. Some positions you can win more quickly, and others more slowly. This comes about because stalemate is still a thing.</p>
  
  <pre><code>
  [title "White to move. (a) mate in 3 moves (b) unroyal: capture king in 2 moves"]  
  [fen "7k/5P2/8/5K2/8/8/8/8 w - - 0 1"]  
  
  </code></pre>
  
  <p>Solution:<br>
  (a) 1. Kf6 Kh7 2. f8=R Kh6 3. Rh8#<br>
  (b) 1. Kg6 Kg8,Kg7,Kh7 2. fxKg8,KxKg7,KxKh7</p>
  
  <pre><code>
  [title "White to move. (a) mate in 1 move (b) unroyal: capture king in 3 moves"]  
  [fen "8/8/8/5N2/K7/8/4p1pp/4Bbrk w - - 0 1"]  
  
  </code></pre>
  
  <p>Solution:<br>
  (a) 1. Ng3#<br>
  (b) 1. Bf2 e1=? 2. Ng3 ~ 3. NxKh1</p>
  
  <p>By the way, does anyone here know a name for this variant of chess where there are no checks or checkmates, and you win by capturing the opponent's king? I'm calling it Unroyal Chess for the purposes of this post. "Checkless chess" is something different. It means that check is illegal <em>unless</em> it ends the game with checkmate.</p>
  
Answers.ContentLicense: CC BY-SA 4.0
Answers.CreationDate: 2018-05-02T14:01:28.723Z
Answers.Text: That second one is an interesting case, playing the move that would usually be checkmate is an error! I think that it would be logical to declare this type of stalemate a loss instead of a draw, if we're doing away with other types of stalemate. It's hardly relevant for practical play anyway.
Answers.UserDisplayName: RemcoGerlich
Answers.ContentLicense: CC BY-SA 4.0
Answers.CreationDate: 2018-05-02T14:42:32.093Z
Answers.Text: @RemcoGerlich: Thanks for this. Stalemate=loss still doesn't give us regular chess, where stalemate is a draw.
Answers.UserDisplayName: Laska
Answers.ContentLicense: CC BY-SA 4.0
Answers.CreationDate: 2018-05-02T06:27:19.417Z
Answers.LastActivityDate: 2018-05-02T06:27:19.417Z
Answers.UserDisplayName: Laska
Answers.Body: <p>Apart from stalemate, what you have to account for is the possibility that both kings are captured in succession, restoring the balance. That's what one of my chess programs did, capturing a defended piece with the king, because the defending pawn was pinned against my king. </p>
  
  <p>So, if the only possible moves are with the king, you need to check whether those are actually legal, or whether the position is stalemate. And when a king is taken, you need to make sure that subsequent moves don't change the evaluation. Apart from that you need to check for checkmate only in the current position, as far as I can see. </p>
  
Answers.ContentLicense: CC BY-SA 3.0
Answers.CreationDate: 2017-01-29T02:06:35.203Z
Answers.Text: I think defining  ±∞ + ∓∞  as  ±∞  would solve this problem.
Answers.UserDisplayName: I. J. Kennedy
Answers.ContentLicense: CC BY-SA 3.0
Answers.CreationDate: 2017-01-30T12:45:22.500Z
Answers.Text: I read "defining victory as simply capturing the opponent's King" as meaning that the game is still over when a king is captured, so successive captures still couldn't happen.
Answers.UserDisplayName: RemcoGerlich
Answers.ContentLicense: CC BY-SA 3.0
Answers.CreationDate: 2017-01-31T10:44:52.670Z
Answers.Text: Sure, I'm just pointing out a possible tripwire in the implementation.
Answers.UserDisplayName: BlindKungFuMaster
Answers.ContentLicense: CC BY-SA 3.0
Answers.CreationDate: 2017-01-28T08:26:52.633Z
Answers.LastActivityDate: 2017-01-28T08:26:52.633Z
Answers.UserDisplayName: BlindKungFuMaster
Answers.Body: <p>If you ignore check/checkmate and do something else, the side giving check would be able to capture the king on the next turn. Therefore, what you are asking is simply the current rules.</p>
  
  <p>Chess AI is already representing the king as infinity internally. You are not changing anything.</p>
  
Answers.ContentLicense: CC BY-SA 3.0
Answers.CreationDate: 2017-01-30T12:43:33.843Z
Answers.Text: This is wrong due to stalemate. With check, K + pawn vs K is often a draw, without check it's always a win (if the defending king can't simply capture the pawn immediately).
Answers.UserDisplayName: RemcoGerlich
Answers.ContentLicense: CC BY-SA 3.0
Answers.CreationDate: 2017-01-28T02:33:26.983Z
Answers.LastActivityDate: 2017-01-28T02:33:26.983Z
Answers.UserDisplayName: SmallChess
Answers.Body: <p>Your "checkless" chess AI would run into problems with the stalemate rule. It would consider the poaition with white king on a6, white pawn a7, black king a8, a win for White because wherever Black moves his king it will get captured. In standard chess, of course, the position is a draw.</p>
  
Answers.ContentLicense: CC BY-SA 3.0
Answers.CreationDate: 2017-01-28T05:49:13.987Z
Answers.LastActivityDate: 2017-01-28T05:49:13.987Z
Answers.UserDisplayName: bof
Body: <p>Is there any material difference between chess the way it is now versus doing away with check and checkmate and defining victory as simply capturing the opponent's King, assuming an available King capture is always taken?</p>
  
  <p>Here is another way way of putting it, along with the motivation for my question: If a chess AI ignored the concepts of check and checkmate, and treated the material value of a King as infinity, would that change its behavior?</p>
  
Tags: <checkmate><chess-variants><programming><check><kings>
Title: Checkless Chess
ThreadText: # Checkless Chess
  
  (Asked by: username_0 on 2017-01-28)
  
  Is there any material difference between chess the way it is now versus doing away with check and checkmate and defining victory as simply capturing the opponent's King, assuming an available King capture is always taken?
  
  Here is another way way of putting it, along with the motivation for my question: If a chess AI ignored the concepts of check and checkmate, and treated the material value of a King as infinity, would that change its behavior?
  
  **Tags:** checkmate, chess-variants, programming, check, kings
  
  
  ---
  
  ## 4 answers
  
  ### Answer by username_5 on 2017-01-28. Score: 12 | Accepted answer
  
  Your "checkless" chess AI would run into problems with the stalemate rule. It would consider the poaition with white king on a6, white pawn a7, black king a8, a win for White because wherever Black moves his king it will get captured. In standard chess, of course, the position is a draw.
  
  
  ---
  
  ### Answer by username_1 on 2018-05-02. Score: 6
  
  This variant is distinct from regular chess. Some positions you can win more quickly, and others more slowly. This comes about because stalemate is still a thing.
  
  [title "White to move. (a) mate in 3 moves (b) unroyal: capture king in 2 moves"]  
  [fen "7k/5P2/8/5K2/8/8/8/8 w - - 0 1"]  
  
  
  Solution:
  (a) 1. Kf6 Kh7 2. f8=R Kh6 3. Rh8#
  (b) 1. Kg6 Kg8,Kg7,Kh7 2. fxKg8,KxKg7,KxKh7
  
  [title "White to move. (a) mate in 1 move (b) unroyal: capture king in 3 moves"]  
  [fen "8/8/8/5N2/K7/8/4p1pp/4Bbrk w - - 0 1"]  
  
  
  Solution:
  (a) 1. Ng3#
  (b) 1. Bf2 e1=? 2. Ng3 ~ 3. NxKh1
  By the way, does anyone here know a name for this variant of chess where there are no checks or checkmates, and you win by capturing the opponent's king? I'm calling it Unroyal Chess for the purposes of this post. "Checkless chess" is something different. It means that check is illegal unless it ends the game with checkmate.
  
  > **Comments:**
  > **username_2**: That second one is an interesting case, playing the move that would usually be checkmate is an error! I think that it would be logical to declare this type of stalemate a loss instead of a draw, if we're doing away with other types of stalemate. It's hardly relevant for practical play anyway.  
  > **username_1**: @username_2: Thanks for this. Stalemate=loss still doesn't give us regular chess, where stalemate is a draw.  
  
  ---
  
  ### Answer by username_3 on 2017-01-28. Score: 2
  
  Apart from stalemate, what you have to account for is the possibility that both kings are captured in succession, restoring the balance. That's what one of my chess programs did, capturing a defended piece with the king, because the defending pawn was pinned against my king.
  
  So, if the only possible moves are with the king, you need to check whether those are actually legal, or whether the position is stalemate. And when a king is taken, you need to make sure that subsequent moves don't change the evaluation. Apart from that you need to check for checkmate only in the current position, as far as I can see.
  
  > **Comments:**
  > **username_0**: I think defining  ±∞ + ∓∞  as  ±∞  would solve this problem.  
  > **username_2**: I read "defining victory as simply capturing the opponent's King" as meaning that the game is still over when a king is captured, so successive captures still couldn't happen.  
  > **username_3**: Sure, I'm just pointing out a possible tripwire in the implementation.  
  
  ---
  
  ### Answer by username_4 on 2017-01-28. Score: 0
  
  If you ignore check/checkmate and do something else, the side giving check would be able to capture the king on the next turn. Therefore, what you are asking is simply the current rules.
  
  Chess AI is already representing the king as infinity internally. You are not changing anything.
  
  > **Comments:**
  > **username_2**: This is wrong due to stalemate. With check, K + pawn vs K is often a draw, without check it's always a win (if the defending king can't simply capture the pawn immediately).  
  
  ---
  
  