Answers.Body: <p>If you include a pawn that has just been promoted to a rook, then yes, it is quite possible to give check with two rooks simultaneously.<br>
  Consider the position where White has Ke1 Re6 e7 g7,  and Black has Ke8 Nf8. White moves 1. exf8(R)++ and gives check with the newly promoted rook as well as the existing rook.<br>
  Checkmate could also be given in this way if, for example, White had a queen on g7 instead of a pawn.</p>
  
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Answers.CreationDate: 2016-05-25T04:55:03.043Z
Answers.LastActivityDate: 2016-05-25T04:55:03.043Z
Answers.UserDisplayName: Jivan Scarano
Answers.Body: <p>For the purposes of writing an algorithm, I don't think I would approach it that way at all.</p>
  
  <p>On any given ply, you generate a list of legal moves to investigate.  A move is illegal if, in the resulting position, your king is in check.  If there are no legal moves, and the king is currently in check, then it's checkmate.  </p>
  
  <p>You don't need an algorithm to figure out whether a check can be blocked or whether the checking piece can be eliminated, or any other scenarios.  The lack of any legal moves in the position indicates that already.</p>
  
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Answers.CreationDate: 2019-08-04T14:11:41.390Z
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Answers.UserDisplayName: adedqwd
Answers.Body: <p>Double check is possible.</p>
  
  <p>One piece must move to deliver a check, while simultaneously allowing another piece to give check that had been blocked by the moving piece.</p>
  
  <p>Examples:</p>
  
  <ul>
  <li>a rook could move on the rank to check on a file while uncovering a bishop check</li>
  <li>a knight could move to give check while uncovering a rook check or a bishop check</li>
  </ul>
  
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Answers.CreationDate: 2016-02-06T04:30:27.213Z
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Answers.LastEditDate: 2016-02-06T09:29:09.463Z
Answers.UserDisplayName: joe sixpak
Answers.Body: <p>If you consider Chinese chess (<a href="https://en.wikipedia.org/wiki/Xiangqi" rel="nofollow noreferrer">Xiang Qi</a>), then technically even triple check is possible.  Imgaine the enemy king, your knight or bishop, your rook and your cannon all in line in that order.  Then if the knight or bishop can move away to give check it is a triple check.  Another difference is that a double check by rook and cannon on the same line could be blocked in one move, so even though technically it is a triple check, because the cannon can leap over the rook, it seems more similar to a double check with respect to blocking.</p>
  
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Answers.CreationDate: 2016-06-12T05:40:23.413Z
Answers.Text: In chess variants that have extra types of pieces like knightriders, triple check is also possible using an en passant capture, because it vacates two squares at the same time.  In a position where White has Kd2, e2, and Black has Kd8, Rd7, d4, and a knightrider on f6, White is in check, and moves 1.e4 blocking the knightrider's attack. Black then moves 1… dxe3 giving check with the pawn, as well as uncovering checks from the knightrider and the rook at the same time.
Answers.UserDisplayName: Jivan Scarano
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Answers.CreationDate: 2016-11-24T00:25:34.547Z
Answers.Text: what is a knightrider??
Answers.UserDisplayName: cascading-style
Answers.ContentLicense: CC BY-SA 3.0
Answers.CreationDate: 2016-11-24T11:44:46.793Z
Answers.Text: A knightrider is a knight that can keep jumping in the same direction as its first knight-jump, similar to how bishop and rook can move as far as they want (and is allowed) in four fixed directions, but cannot change direction mid-move.
Answers.UserDisplayName: hkBst
Answers.ContentLicense: CC BY-SA 3.0
Answers.CreationDate: 2018-04-08T14:54:21.217Z
Answers.Text: It is also possible to quadruple-check in Chinese chess
Answers.UserDisplayName: David Ni
Answers.ContentLicense: CC BY-SA 4.0
Answers.CreationDate: 2019-08-05T20:50:58.607Z
Answers.Text: @Derek 朕會功夫  I think you can do something like, move a chariot to uncover checks from two horses, while also giving check with the chariot and enabling a check from a cannon.
Answers.UserDisplayName: adedqwd
Answers.ContentLicense: CC BY-SA 4.0
Answers.CreationDate: 2019-05-16T15:56:26.013Z
Answers.Text: @DavidNi I’m quite curious - is there an example of such move?
Answers.UserDisplayName: Derek 朕會功夫
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Answers.CreationDate: 2016-05-25T07:42:01.193Z
Answers.LastActivityDate: 2019-08-03T19:09:59.290Z
Answers.LastEditDate: 2019-08-03T19:09:59.290Z
Answers.UserDisplayName: hkBst
Answers.Body: <p>The King can be checked by multiple pieces via a double check tactic. Consider the following position:</p>
  
  <p>White Queen on g4, White Rook on f5, Black King on d7.</p>
  
  <p>White plays 1. Rf7+, and Black's King is checked by both White's Rook and Queen.</p>
  
  <p>For your algorithm, it would be checkmate if BOTH pieces cannot be blocked, taken, avoided, etc. Consider the following:</p>
  
  <ol>
  <li>e4 e6 2. Nc3 d5 3. exd5 exd5 4.d3 d4 5. Ne4 Nc6 6. Qe2 Bg4 7. Nf6#</li>
  </ol>
  
  <p>The final position is a double check and checkmate. Notice how both White's Queen and Knight can be taken or avoided, if you consider them individually. However, they cannot BOTH be taken/avoided/blocked, so Black is checkmated.</p>
  
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Answers.CreationDate: 2018-04-06T18:31:13.393Z
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Answers.UserDisplayName: Inertial Ignorance
Answers.Body: <p>Actually, there is a way for 2 queens to be discovered simultaneously-by the en passant double check. A very rare form of the double check, the en passant double check discovers 2 checking pieces (a rook and bishop) simultaneously. Either can be a queen, both can be queens, or both can be non queens. This is one of my favorite double checks. Also one of my favorites is the pawn-pinned piece double check (a king-pawn-pinned piece would be up there, but that's impossible).</p>
  
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Answers.CreationDate: 2024-10-01T01:26:14.793Z
Answers.LastActivityDate: 2024-10-01T01:26:14.793Z
Answers.UserDisplayName: Joe Peters
Answers.Body: <p>In standard chess, you can illegally can check a king 8 times at once. Consider 8 knights a that are leap away from the enemy king. </p>
  
  <pre><code>[FEN "4k3/8/3n1n2/2n3n1/4K3/2n3n1/3n1n2/8 w - - 0 1"]
  </code></pre>
  
  <p>The king still has his orthogonal moves left, and is now 1 move away from attacking 2 of the knights. Since both of them are unprotected, one of the 8 knights may move to where the king was, to protect all 7 other knights. The King is not necessarily trapped, but certainly not free.</p>
  
Answers.ContentLicense: CC BY-SA 3.0
Answers.CreationDate: 2016-11-21T20:51:01.870Z
Answers.Text: I don't understand what you are trying to say. This question is about multiple checks, i.e. the king is attacked by more than one piece at the same time. The scenario you describe (8 knights attacking a king) is impossible to reach in standard chess.
Answers.UserDisplayName: user1583209
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Answers.Text: I DID SAY IT IS IMPRACTICAL! a, and b: I gave a scenario that, although impractical to attain in standard chess, is a counter example of the question.
Answers.UserDisplayName: Garrison Pendergrass
Answers.ContentLicense: CC BY-SA 3.0
Answers.CreationDate: 2016-11-24T00:26:44.877Z
Answers.Text: maybe post a diagram of whatever you are trying to say.
Answers.UserDisplayName: cascading-style
Answers.ContentLicense: CC BY-SA 4.0
Answers.CreationDate: 2019-08-09T14:12:46.953Z
Answers.Text: @RewanDemontay That isnt impractical, it is an illegal position. If the white king is already in check, it must move immediately - it can't wait 7 more moves for the rest of the knights to get in place.
Answers.UserDisplayName: Grade 'Eh' Bacon
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Answers.Text: @RewanDemontay Sorry, I @ Pinged you but meant to ping Garrison - agreed this is an illegal position and therefore the answer doesn't properly address the question. Although I will add that editing an answer post to reflect a refutation of the answerer's opinion is a little confusing and should not be done, as edits should not disagree with the intent of the author.
Answers.UserDisplayName: Grade 'Eh' Bacon
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Answers.LastEditDate: 2019-08-03T19:55:01.353Z
Answers.UserDisplayName: Garrison Pendergrass
Answers.Body: <p>Double check is a fine tactic. An example would be a bishop lined up on the same diagonal as the king with a rook or knight in the way blocking the check. The rook or knight moves giving check to the king and also uncovering the check from the bishop. The king must move since there is no way to block two different lines or take two different pieces at the same time. </p>
  
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Answers.CreationDate: 2016-02-05T00:09:11.817Z
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Answers.UserDisplayName: Brian Towers
Body: <p>I am writing a simple chess game in which I have to determine the end game conditions. My algorithm requires the piece that is putting the opponent king in check, and checks the following:</p>
  
  <ul>
  <li>King cannot escape</li>
  <li>Piece cannot be eliminated</li>
  <li>Path cannot be blocked</li>
  </ul>
  
  <p>If all three conditions satisfy, then it is checkmate. However, I am wondering if there can be more than one piece simultaneously putting a king in check. It doesn't seem to be possible, but I can't come up with a proof for it. For example, is it possible for 2 rooks to put a king in check at the same time? Personally, I don't think that it's possible.</p>
  
Comments.ContentLicense: CC BY-SA 3.0
Comments.CreationDate: 2016-02-05T08:59:03.123Z
Comments.Text: It is not possible with two rooks (or any two pieces of the same kind) because the two pieces have to move differenty. The first has to block the second in the beginning and after that needs to give check himself, as is explained in the answer.
Comments.UserDisplayName: chaosflaws
Comments.ContentLicense: CC BY-SA 4.0
Comments.CreationDate: 2024-10-01T02:56:20.507Z
Comments.Text: It is actually possible to have a two-Rook double check,
  though it must be rare.  A two-Queen double check is reasonably common.
  In each case one of the checking pieces has just promoted.
  (ETA: I see now that **Jivan Scarano** already observed this eight years ago . . .
  and **Joe Peters**'s answer notes the additional possibility of *en passant*
  giving a double check from two Queens; I'd expect this to be even rarer than
  the RR setup.)
Comments.UserDisplayName: Noam D. Elkies
Tags: <rules><checkmate><check>
Title: Is it true that at any time only one piece can put king in check?
ThreadText: # Is it true that at any time only one piece can put king in check?
  
  (Asked by: username_0 on 2016-02-05)
  
  I am writing a simple chess game in which I have to determine the end game conditions. My algorithm requires the piece that is putting the opponent king in check, and checks the following:
  
  * King cannot escape
  * Piece cannot be eliminated
  * Path cannot be blocked
  
  If all three conditions satisfy, then it is checkmate. However, I am wondering if there can be more than one piece simultaneously putting a king in check. It doesn't seem to be possible, but I can't come up with a proof for it. For example, is it possible for 2 rooks to put a king in check at the same time? Personally, I don't think that it's possible.
  
  **Tags:** rules, checkmate, check
  
  > **Comments:**
  > **username_1**: It is not possible with two rooks (or any two pieces of the same kind) because the two pieces have to move differenty. The first has to block the second in the beginning and after that needs to give check himself, as is explained in the answer.  
  > **username_2**: It is actually possible to have a two-Rook double check, though it must be rare.  A two-Queen double check is reasonably common. In each case one of the checking pieces has just promoted. (ETA: I see now that **username_3** already observed this eight years ago . . . and **username_10**'s answer notes the additional possibility of *en passant* giving a double check from two Queens; I'd expect this to be even rarer than the RR setup.)  
  
  ---
  
  ## 8 answers
  
  ### Answer by username_14 on 2016-02-05. Score: 25 | Accepted answer
  
  Double check is a fine tactic. An example would be a bishop lined up on the same diagonal as the king with a rook or knight in the way blocking the check. The rook or knight moves giving check to the king and also uncovering the check from the bishop. The king must move since there is no way to block two different lines or take two different pieces at the same time.
  
  
  ---
  
  ### Answer by username_3 on 2016-05-25. Score: 12
  
  If you include a pawn that has just been promoted to a rook, then yes, it is quite possible to give check with two rooks simultaneously.  
  Consider the position where White has Ke1 Re6 e7 g7, and Black has Ke8 Nf8. White moves 1. exf8(R)++ and gives check with the newly promoted rook as well as the existing rook.  
  Checkmate could also be given in this way if, for example, White had a queen on g7 instead of a pawn.
  
  
  ---
  
  ### Answer by username_4 on 2019-08-04. Score: 9
  
  For the purposes of writing an algorithm, I don't think I would approach it that way at all.
  
  On any given ply, you generate a list of legal moves to investigate. A move is illegal if, in the resulting position, your king is in check. If there are no legal moves, and the king is currently in check, then it's checkmate.
  
  You don't need an algorithm to figure out whether a check can be blocked or whether the checking piece can be eliminated, or any other scenarios. The lack of any legal moves in the position indicates that already.
  
  
  ---
  
  ### Answer by username_5 on 2016-02-06. Score: 6
  
  Double check is possible.
  
  One piece must move to deliver a check, while simultaneously allowing another piece to give check that had been blocked by the moving piece.
  
  Examples:
  
  * a rook could move on the rank to check on a file while uncovering a bishop check
  * a knight could move to give check while uncovering a rook check or a bishop check
  
  
  ---
  
  ### Answer by username_6 on 2016-05-25. Score: 5
  
  If you consider Chinese chess ([Xiang Qi](https://en.wikipedia.org/wiki/Xiangqi)), then technically even triple check is possible. Imgaine the enemy king, your knight or bishop, your rook and your cannon all in line in that order. Then if the knight or bishop can move away to give check it is a triple check. Another difference is that a double check by rook and cannon on the same line could be blocked in one move, so even though technically it is a triple check, because the cannon can leap over the rook, it seems more similar to a double check with respect to blocking.
  
  > **Comments:**
  > **username_3**: In chess variants that have extra types of pieces like knightriders, triple check is also possible using an en passant capture, because it vacates two squares at the same time.  In a position where White has Kd2, e2, and Black has Kd8, Rd7, d4, and a knightrider on f6, White is in check, and moves 1.e4 blocking the knightrider's attack. Black then moves 1… dxe3 giving check with the pawn, as well as uncovering checks from the knightrider and the rook at the same time.  
  > **username_7**: what is a knightrider??  
  > **username_6**: A knightrider is a knight that can keep jumping in the same direction as its first knight-jump, similar to how bishop and rook can move as far as they want (and is allowed) in four fixed directions, but cannot change direction mid-move.  
  > **username_8**: It is also possible to quadruple-check in Chinese chess  
  > **username_0**: @DavidNi I’m quite curious - is there an example of such move?  
  > **username_4**: @username_0  I think you can do something like, move a chariot to uncover checks from two horses, while also giving check with the chariot and enabling a check from a cannon.  
  
  ---
  
  ### Answer by username_9 on 2018-04-06. Score: 2
  
  The King can be checked by multiple pieces via a double check tactic. Consider the following position:
  
  White Queen on g4, White Rook on f5, Black King on d7.
  
  White plays 1. Rf7+, and Black's King is checked by both White's Rook and Queen.
  
  For your algorithm, it would be checkmate if BOTH pieces cannot be blocked, taken, avoided, etc. Consider the following:
  
  1. e4 e6 2. Nc3 d5 3. exd5 exd5 4.d3 d4 5. Ne4 Nc6 6. Qe2 Bg4 7. Nf6#
  
  The final position is a double check and checkmate. Notice how both White's Queen and Knight can be taken or avoided, if you consider them individually. However, they cannot BOTH be taken/avoided/blocked, so Black is checkmated.
  
  
  ---
  
  ### Answer by username_10 on 2024-10-01. Score: 1
  
  Actually, there is a way for 2 queens to be discovered simultaneously-by the en passant double check. A very rare form of the double check, the en passant double check discovers 2 checking pieces (a rook and bishop) simultaneously. Either can be a queen, both can be queens, or both can be non queens. This is one of my favorite double checks. Also one of my favorites is the pawn-pinned piece double check (a king-pawn-pinned piece would be up there, but that's impossible).
  
  
  ---
  
  ### Answer by username_11 on 2016-11-21. Score: -6
  
  In standard chess, you can illegally can check a king 8 times at once. Consider 8 knights a that are leap away from the enemy king. 
  [FEN "4k3/8/3n1n2/2n3n1/4K3/2n3n1/3n1n2/8 w - - 0 1"]
  
  The king still has his orthogonal moves left, and is now 1 move away from attacking 2 of the knights. Since both of them are unprotected, one of the 8 knights may move to where the king was, to protect all 7 other knights. The King is not necessarily trapped, but certainly not free.
  
  > **Comments:**
  > **username_12**: I don't understand what you are trying to say. This question is about multiple checks, i.e. the king is attacked by more than one piece at the same time. The scenario you describe (8 knights attacking a king) is impossible to reach in standard chess.  
  > **username_11**: I DID SAY IT IS IMPRACTICAL! a, and b: I gave a scenario that, although impractical to attain in standard chess, is a counter example of the question.  
  > **username_7**: maybe post a diagram of whatever you are trying to say.  
  > **username_13**: @RewanDemontay That isnt impractical, it is an illegal position. If the white king is already in check, it must move immediately - it can't wait 7 more moves for the rest of the knights to get in place.  
  > **username_13**: @RewanDemontay Sorry, I @ Pinged you but meant to ping Garrison - agreed this is an illegal position and therefore the answer doesn't properly address the question. Although I will add that editing an answer post to reflect a refutation of the answerer's opinion is a little confusing and should not be done, as edits should not disagree with the intent of the author.  
  
  ---
  
  