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Pin
,Created page with "'''Home * Chess * Tactics * Pin''' A '''Pin''' is a X-ray related situation where a sliding piece, a bishop, a Rook|..."
'''[[Main Page|Home]] * [[Chess]] * [[Tactics]] * Pin'''
A '''Pin''' is a [[X-ray]] related situation where a [[Sliding Pieces|sliding piece]], a [[Bishop|bishop]], a [[Rook|rook]] or a [[Queen|queen]] indirectly attacks an opponent [[King|king]] or piece potentially [[En prise|en prise]], shielded by another directly attacked opponent piece or pawn on the attacking [[Rays|ray]]. The direct attacked piece or pawn is then called '''pinned''', and cannot move out of the line of attack, without leaving the indirectly attacked piece [[En prise|en prise]] or illegally its own king in [[Check|check]]. All pieces except the king may be pinned. One tactic which takes advantage of a pin is called ''working the pin'', where other pieces from the pinning piece's side attack the opposing pinned piece.
<span id="AbsolutePin"></span>
=Types=
==Absolute Pin==
The absolute pin is where the piece shielded by the pinned piece is the king. In chess programming, to detect absolute pins is necessary for [[Legal Move|legal]] [[Move Generation|move generation]] and may be considered in [[Evaluation|evaluation]].
<span id="PartialPin"></span>
==Partial Pin==
A partial pin refers to (absolute) pins, where the pinned piece or pawn can move along the attacking [[Direction|direction]], and may even capture the pinning sliding piece.
<span id="RelativePin"></span>
==Relative Pin==
A relative pin is where the piece shielded by the pinned piece is not the king, but either a more valuable than the pinned piece, or conditionally en prise.
==Cross Pin==
A cross pin describes the rare case, where one piece is pinned in multiple directions simultaneously, most often one partial pin shielding the king and a relative pin shielding the queen. For instance in the otherwise harmless case of a partial pin of a bishop by a bishop, the bishop is also shielding a otherwise hanging queen by a queen, same may apply for rooks instead of bishops. Here the black rook on e4 is cross pinned and black will lose material and likely the game:
<fentt border="double" style="font-size:24pt">4k3/1p4pp/2p5/8/q3r2Q/3p3P/1P4PK/4R3</fentt>
4k3/1p4pp/2p5/8/q3r2Q/3p3P/1P4PK/4R3 b - -
Of course with the white king on g1 or h1, things would be different. Such multiple issue tactics seems all the domain of the [[Search|search]] and is hard to evaluate statically.
==Situational Pin==
This kind of relative pin is not about shielding own pieces, but important squares, for instance where an opponent rook may have a [[Mate at a Glance#MatesWithSlidingPieces|back rank mate]]. This kind of pins are usually only considered implicit by the search.
=Considering Pins=
Pinned pieces may be considered inside a chess program's [[Move Generation|move generation]] and [[Evaluation|evaluation]].
==Move Generation==
[[Legal Move]] generation requires information about absolute pinned pieces, and their pinning direction to cover partial pins. Even non strictly legal move generation may reduce the number of generated illegal moves if considering absolute and partial pinnes, while ignoring the legality of [[En passant]] captures and [[Castling|castling]].
==Evaluation==
Evaluation can take the restricted [[Mobility|mobility]] of pinned pieces into account, and should consider the [[Distance|distance]] of the pinned pieces to its shielded king (or queen for relative pins) and whether it is on the own or opponent half of the board during the [[Opening|opening]] or [[Middlegame|middlegame]]. Some programs even calculate on ''working the pin'', to look whether pinned pieces may further attacked by other pieces, especially pawns, for instance with [[Bitboards|bitboards]] whether they [[General Setwise Operations#Intersection|intersect]] opponent none-guarded pawn [[Attack Spans|front attack spans]] and assign appropriate evaluation penalties.
=See also=
* [[Checks and Pinned Pieces (Bitboards)]]
* [[En passant]]
* [[Legal Move]]
* [[Move Generation]]
* [[Skewer]]
* [[Sliding Piece Attacks]]
* [[X-ray]]
* [[X-ray Attacks (Bitboards)]]
=Forum Posts=
==2000 ...==
* [https://www.stmintz.com/ccc/index.php?id=306311 Question about the KnightCap find_pins function] by Matthew White, [[CCC]], July 14, 2003 » [[KnightCap]]
* [https://www.stmintz.com/ccc/index.php?id=366095 Evaluating Pinned Pieces] by [[Tom Likens]], [[CCC]], May 19, 2004
* [https://www.stmintz.com/ccc/index.php?id=385126 SEE and pin detection] by [[Dan Honeycutt]], [[CCC]], August 30, 2004 » [[Static Exchange Evaluation]]
* [https://www.stmintz.com/ccc/index.php?id=390108 Pin aware SEE] by [[Dan Honeycutt]], [[CCC]], October 03, 2004
* [http://www.talkchess.com/forum/viewtopic.php?t=22550 Bitboard of Pinned Pieces] by [[Grant Osborne]], [[CCC]], July 24, 2008
==2010 ...==
* [http://www.talkchess.com/forum/viewtopic.php?topic_view=threads&p=395213 LVA MVV with relative Pin] by [[Clemens Pruell]], [[CCC]], February 16, 2011 » [[MVV-LVA]]
* [http://www.talkchess.com/forum/viewtopic.php?t=40597 pinned pieces in eval] by Pierre Bokma, [[CCC]], October 01, 2011
=External Links=
* [https://en.wikipedia.org/wiki/Pin_%28chess%29 Pin (chess) from Wikipedia]
* [http://www.top10chess.com/2008/09/tactical-motif-vii-pin.html Top 10 chess: Tactical Motif VII: The pin]
* [http://www.chesstactics.org/index.php?Type=page&Action=none&From=4,1,1,1 The Pin and the Skewer] from [http://www.chesstactics.org/ Ward Farnsworth's Predator at the Chessboard]
'''[[Tactics|Up one Level]]'''
A '''Pin''' is a [[X-ray]] related situation where a [[Sliding Pieces|sliding piece]], a [[Bishop|bishop]], a [[Rook|rook]] or a [[Queen|queen]] indirectly attacks an opponent [[King|king]] or piece potentially [[En prise|en prise]], shielded by another directly attacked opponent piece or pawn on the attacking [[Rays|ray]]. The direct attacked piece or pawn is then called '''pinned''', and cannot move out of the line of attack, without leaving the indirectly attacked piece [[En prise|en prise]] or illegally its own king in [[Check|check]]. All pieces except the king may be pinned. One tactic which takes advantage of a pin is called ''working the pin'', where other pieces from the pinning piece's side attack the opposing pinned piece.
<span id="AbsolutePin"></span>
=Types=
==Absolute Pin==
The absolute pin is where the piece shielded by the pinned piece is the king. In chess programming, to detect absolute pins is necessary for [[Legal Move|legal]] [[Move Generation|move generation]] and may be considered in [[Evaluation|evaluation]].
<span id="PartialPin"></span>
==Partial Pin==
A partial pin refers to (absolute) pins, where the pinned piece or pawn can move along the attacking [[Direction|direction]], and may even capture the pinning sliding piece.
<span id="RelativePin"></span>
==Relative Pin==
A relative pin is where the piece shielded by the pinned piece is not the king, but either a more valuable than the pinned piece, or conditionally en prise.
==Cross Pin==
A cross pin describes the rare case, where one piece is pinned in multiple directions simultaneously, most often one partial pin shielding the king and a relative pin shielding the queen. For instance in the otherwise harmless case of a partial pin of a bishop by a bishop, the bishop is also shielding a otherwise hanging queen by a queen, same may apply for rooks instead of bishops. Here the black rook on e4 is cross pinned and black will lose material and likely the game:
<fentt border="double" style="font-size:24pt">4k3/1p4pp/2p5/8/q3r2Q/3p3P/1P4PK/4R3</fentt>
4k3/1p4pp/2p5/8/q3r2Q/3p3P/1P4PK/4R3 b - -
Of course with the white king on g1 or h1, things would be different. Such multiple issue tactics seems all the domain of the [[Search|search]] and is hard to evaluate statically.
==Situational Pin==
This kind of relative pin is not about shielding own pieces, but important squares, for instance where an opponent rook may have a [[Mate at a Glance#MatesWithSlidingPieces|back rank mate]]. This kind of pins are usually only considered implicit by the search.
=Considering Pins=
Pinned pieces may be considered inside a chess program's [[Move Generation|move generation]] and [[Evaluation|evaluation]].
==Move Generation==
[[Legal Move]] generation requires information about absolute pinned pieces, and their pinning direction to cover partial pins. Even non strictly legal move generation may reduce the number of generated illegal moves if considering absolute and partial pinnes, while ignoring the legality of [[En passant]] captures and [[Castling|castling]].
==Evaluation==
Evaluation can take the restricted [[Mobility|mobility]] of pinned pieces into account, and should consider the [[Distance|distance]] of the pinned pieces to its shielded king (or queen for relative pins) and whether it is on the own or opponent half of the board during the [[Opening|opening]] or [[Middlegame|middlegame]]. Some programs even calculate on ''working the pin'', to look whether pinned pieces may further attacked by other pieces, especially pawns, for instance with [[Bitboards|bitboards]] whether they [[General Setwise Operations#Intersection|intersect]] opponent none-guarded pawn [[Attack Spans|front attack spans]] and assign appropriate evaluation penalties.
=See also=
* [[Checks and Pinned Pieces (Bitboards)]]
* [[En passant]]
* [[Legal Move]]
* [[Move Generation]]
* [[Skewer]]
* [[Sliding Piece Attacks]]
* [[X-ray]]
* [[X-ray Attacks (Bitboards)]]
=Forum Posts=
==2000 ...==
* [https://www.stmintz.com/ccc/index.php?id=306311 Question about the KnightCap find_pins function] by Matthew White, [[CCC]], July 14, 2003 » [[KnightCap]]
* [https://www.stmintz.com/ccc/index.php?id=366095 Evaluating Pinned Pieces] by [[Tom Likens]], [[CCC]], May 19, 2004
* [https://www.stmintz.com/ccc/index.php?id=385126 SEE and pin detection] by [[Dan Honeycutt]], [[CCC]], August 30, 2004 » [[Static Exchange Evaluation]]
* [https://www.stmintz.com/ccc/index.php?id=390108 Pin aware SEE] by [[Dan Honeycutt]], [[CCC]], October 03, 2004
* [http://www.talkchess.com/forum/viewtopic.php?t=22550 Bitboard of Pinned Pieces] by [[Grant Osborne]], [[CCC]], July 24, 2008
==2010 ...==
* [http://www.talkchess.com/forum/viewtopic.php?topic_view=threads&p=395213 LVA MVV with relative Pin] by [[Clemens Pruell]], [[CCC]], February 16, 2011 » [[MVV-LVA]]
* [http://www.talkchess.com/forum/viewtopic.php?t=40597 pinned pieces in eval] by Pierre Bokma, [[CCC]], October 01, 2011
=External Links=
* [https://en.wikipedia.org/wiki/Pin_%28chess%29 Pin (chess) from Wikipedia]
* [http://www.top10chess.com/2008/09/tactical-motif-vii-pin.html Top 10 chess: Tactical Motif VII: The pin]
* [http://www.chesstactics.org/index.php?Type=page&Action=none&From=4,1,1,1 The Pin and the Skewer] from [http://www.chesstactics.org/ Ward Farnsworth's Predator at the Chessboard]
'''[[Tactics|Up one Level]]'''
