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'''[[Main Page|Home]] * [[Chess]] * Fortress'''
[[FILE:Карта-схема к статье «Креста Святого крепость» № 2. Военная энциклопедия Сытина (Санкт-Петербург, 1911-1915).jpg|border|right|thumb| Russian Fortress <ref>A Russian Fortress (1722-1733) at the junction of the rivers Agrakhani and [https://en.wikipedia.org/wiki/Sulak_River Sulak] near the [https://en.wikipedia.org/wiki/Caspian_Sea Caspian Sea] in [https://en.wikipedia.org/wiki/Dagestan Dagestan], at the former western boarder of the [https://en.wikipedia.org/wiki/Tsardom_of_Russia Tsardom of Russia] to [https://en.wikipedia.org/wiki/Iran Persia] of the [https://en.wikipedia.org/wiki/Safavid_dynasty Safavid dynasty], founded by [https://en.wikipedia.org/wiki/Peter_the_Great Peter the Great] while launching the [https://en.wikipedia.org/wiki/Russo-Persian_War_(1722%E2%80%931723) Russo-Persian War], source [https://ru.wikisource.org/wiki/%D0%92%D0%AD/%D0%92%D0%A2/%D0%9A%D1%80%D0%B5%D1%81%D1%82%D0%B0_%D0%A1%D0%B2%D1%8F%D1%82%D0%BE%D0%B3%D0%BE_%D0%BA%D1%80%D0%B5%D0%BF%D0%BE%D1%81%D1%82%D1%8C ВЭ/ВТ/Креста Святого крепость — Викитека] (VE / BT / Cross of the Holy Fortress - Wikisource, [https://www.wikidata.org/wiki/Q4114391 Sytin Military Encyclopedia], [https://en.wikipedia.org/wiki/Saint_Petersburg St. Petersburg], 1911-1915)</ref> ]]
'''Fortress''',<br/>
an [[Endgame|endgame]] drawing technique where a side usually behind in [[Material|material]] sets up a zone of protection that the opponent cannot penetrate <ref>[https://en.wikipedia.org/wiki/Fortress_(chess) Fortress (chess) from Wikipedia]</ref>. While fortresses are quite common in (late) endgames, f.i. in [[Wrong Color Bishop and Rook Pawn]], fortresses may rarely occur in the (late) [[Middlegame|middlegame]], characterized by long fixed [[Pawn Chain|pawn chains]] with up to one or two [[Open File|open files]] but all points of penetration well defended by the weaker side. Chess programs without the implemetation of special knowledge typically fail to recognize fortresses and seem to claim a [[Pawn Advantage, Win Percentage, and Elo|winning advantage]], although they are not able to achieve the win against adequate defence <ref>[[Matej Guid]], [[Ivan Bratko]] ('''2012'''). ''Detecting Fortresses in Chess''. [http://ev.fe.uni-lj.si/ Elektrotehniški vestnik], Vol. 79, Nos. 1-2, [https://ailab.si/matej/doc/Detecting_Fortresses_in_Chess.pdf pdf]</ref>.
=Fortress Detection=
==Evaluation==
Fortress detection might be triggered in [[Evaluation|evaluation]] or [[Interior Node Recognizer|interior node recognizers]] if certain material configurations along with the winning advantage, and [[Pawn Structure|pawn structure]] properties occur. Further [[Pattern Matching|pattern matching]] considering relevant features of fortress positions or fuzzier [[Pattern Recognition|pattern recognition]] is then used to scale the winning advantage towards the [[Score#DrawScore|draw score]] zero - the fuzzier and possibly more error-prone the heuristics, the less the draw scaling. However, due to [[Knowledge#SearchversusKnowledge|search versus knowledge trade-off]], and all that generalization and [[Automated Tuning|tuning]] problems involved with adding knowledge and noise, practical [[Playing Strength|playing strength]] versus usefulness in analysis is an issue.
==Sample==
A pattern of rook vs queen fortress in the endgame was given by [[Lyudmil Tsvetkov]] in his 2017 ''The Secret of Chess'' <ref>[[Lyudmil Tsvetkov]] ('''2017'''). ''[http://www.secretofchess.com/ The Secret of Chess]''. [https://www.amazon.com/Secret-Chess-Lyudmil-Tsvetkov-ebook/dp/B074M85CVV amazon] - Rook vs queen fortress in the endgame, pp. 273</ref>:
One side having just one queen, and at most a single pawn, with the other having just one rook, and at least one pawn, if the queen side has no passers, the rook is protected by a pawn on the g or b files on its 2nd rank, the king of the rook side is adjacent to that pawn, the pawn of the queen side is on files h,f,a or c, and the king of the queen side is not past its 5th rank.
==Search==
Another technique of fortress detection as proposed by [[Matej Guid]] and [[Ivan Bratko]] in 2012 <ref>[[Matej Guid]], [[Ivan Bratko]] ('''2012'''). ''Detecting Fortresses in Chess''. [http://ev.fe.uni-lj.si/ Elektrotehniški vestnik], Vol. 79, Nos. 1-2, [https://ailab.si/matej/doc/Detecting_Fortresses_in_Chess.pdf pdf]</ref> is related to [[Search|search]], in particular [[Iterative Deepening|iterative deepening]] along with "no progress" indication - that is the root evaluation or low search depths already indicate a winning score, which is not increasing in consecutive iterations. A few programs start scaling scores toward zero if the [[Halfmove Clock|halfmove clock]] already exceeds values far below enforcing the [[Fifty-move Rule|50 move rule]], often triggered by conditions mentioned above. Matej Guid and Ivan Bratko further mention the possibility of [[Monte-Carlo Tree Search]] to detect fortresses.
=See also=
* [[Bishops of Opposite Colors]]
* [[Blockade]]
* [[Blockage Detection]]
* [[Draw]]
* [[Draw Evaluation]]
* [[Score#DrawScore|Draw Scores]]
* [[Fortress (Engine)]]
* [[Material#InsufficientMaterial|Insufficient Material]]
* [[Pattern Recognition]]
* [[Check#Perpetual|Perpetual Check]]
* [[Repetitions]]
* [[Stalemate]]
* [[Wrong Color Bishop and Rook Pawn]]
=Selected Publications=
* [[Karsten Müller]], [https://ratings.fide.com/card.phtml?event=4622170 Wolfgang Pajeken] ('''2008'''). ''How to Play Chess Endings''. [https://en.wikipedia.org/wiki/Gambit_Publications Gambit Publications], [https://www.amazon.com/Play-Chess-Endgames-Karsten-Muller/dp/1904600867 amazon], Chapter 11
* [[Lyudmil Tsvetkov]] ('''2010'''). ''Little Chess Evaluation Compendium''. [http://www.winboardengines.de/doc/LittleChessEvaluationCompendium-2010-04-07.pdf 2010 pdf]
* [[Matej Guid]], [[Ivan Bratko]] ('''2012'''). ''Detecting Fortresses in Chess''. [http://ev.fe.uni-lj.si/ Elektrotehniški vestnik], Vol. 79, Nos. 1-2, [https://ailab.si/matej/doc/Detecting_Fortresses_in_Chess.pdf pdf] » [[Rybka]], [[Houdini]] <ref>[http://www.talkchess.com/forum/viewtopic.php?t=64306&start=27 Re: Tony's positional test suite] by [[Louis Zulli]], [[CCC]], August 01, 2017</ref>
* [[Lyudmil Tsvetkov]] ('''2017'''). ''[http://www.secretofchess.com/ The Secret of Chess]''. [https://www.amazon.com/Secret-Chess-Lyudmil-Tsvetkov-ebook/dp/B074M85CVV amazon]
=Forum Posts=
==2000 ...==
* [https://www.stmintz.com/ccc/index.php?id=218993 Thanks -- and a question about "fortress" recognition in programs] by Steve, [[CCC]], March 21, 2002
* [https://www.stmintz.com/ccc/index.php?id=269953 The Bahrain Fortress] by [[Michael Scheidl|Mike Scheidl]], December 10, 2002 » [[Kramnik versus Deep Fritz 2002#6|Kramnik versus Deep Fritz 2002 - Game 6]]
* [https://www.stmintz.com/ccc/index.php?id=378332 missing a win or fortress?] by [[Uri Blass]], [[CCC]], July 21, 2004
==2005 ...==
* [https://www.stmintz.com/ccc/index.php?id=471530 Fortress: is there an engine that can solve this?] by Peter Kasinski, [[CCC]], December 18, 2005
* [http://www.talkchess.com/forum/viewtopic.php?t=13872 Is this positions drawn ?] by M. Ansari, [[CCC]], May 18, 2007
* [http://www.talkchess.com/forum/viewtopic.php?t=23109 Fortress detection program] by Anil, [[CCC]], August 19, 2008
* [http://www.talkchess.com/forum/viewtopic.php?t=28193 Fortress Draws] by [http://www.talkchess.com/forum/profile.php?mode=viewprofile&u=608 Ted Summers], [[CCC]], May 31, 2009
==2010 ...==
* [http://www.talkchess.com/forum/viewtopic.php?t=32034 Funny fortress position] by [[Joona Kiiski]], [[CCC]], January 25, 2010
* [http://www.open-chess.org/viewtopic.php?f=5&t=1015 "No progress" and Graph History Interaction] by [[Mark Watkins|BB+]], [[Computer CHess Forums|OpenChess Forum]], January 23, 2011 » [[Graph History Interaction]]
* [http://www.talkchess.com/forum/viewtopic.php?t=38402 Another fortress position] by Robert Flesher, [[CCC]], March 13, 2011
* [http://www.talkchess.com/forum/viewtopic.php?t=44300 Simple fortress detection, engines fail] by [[Vincent Lejeune]], [[CCC]], July 04, 2012
* [http://www.talkchess.com/forum/viewtopic.php?t=46245 test position: fortress] by [[Jon Dart]], [[CCC]], December 02, 2012
* [http://www.talkchess.com/forum/viewtopic.php?t=47907 Idea for recognizing fortress/encouraging progress] by Piotr Lopusiewicz, [[CCC]], May 03, 2013
* [http://www.talkchess.com/forum/viewtopic.php?topic_view=threads&p=601224&t=54697 Re: Chessprogams with the most chessknowing] by [[Ferdinand Mosca]], [[CCC]], December 20, 2014
==2015 ...==
* [http://www.talkchess.com/forum/viewtopic.php?t=55773 Endgame fortress handling] by [[Lyudmil Tsvetkov]], [[CCC]], March 25, 2015
* [http://www.talkchess.com/forum/viewtopic.php?t=59025 A very subtle fortress destruction] by [[Árpád Rusz]], [[CCC]], January 23, 2016
* [http://www.talkchess.com/forum/viewtopic.php?t=59264 Fortresses] by [[Jon Fredrik Åsvang]], [[CCC]], February 15, 2016
* [http://www.talkchess.com/forum/viewtopic.php?t=62976 Fortresses] by [[Jon Fredrik Åsvang]], [[CCC]], January 30, 2017
* [http://www.talkchess.com/forum/viewtopic.php?t=65247 What does semi-fortress mean?] by [[Jon Fredrik Åsvang]], [[CCC]], September 22, 2017
* [http://www.talkchess.com/forum/viewtopic.php?t=66413 replace the evaluation by playing against yourself] by [[Uri Blass]], [[CCC]], January 25, 2018 » [[Evaluation]]
=External Links=
==On Topic==
* [https://en.wikipedia.org/wiki/Fortress_(chess) Fortress (chess) from Wikipedia]
* [https://chess24.com/en/read/glossary/fortress Fortress - chess term] | [https://en.wikipedia.org/wiki/Chess24.com chess24.com]
* [https://lichess.org/video/SOzdwycf8y0 A Rare Chess Fortress: Queen vs. Bishop & Knight Endgame • Free Chess Videos • lichess.org]
* [https://lichess.org/video/ZsCt9sG6oig? Endgame Fortresses • Free Chess Videos • lichess.org] by [https://en.wikipedia.org/wiki/Varuzhan_Akobian GM Varuzhan Akobian], January 13, 2015
==Misc==
* [https://en.wikipedia.org/wiki/Fortress_chess Fortress chess (variant) from Wikipedia]
* [https://en.wikipedia.org/wiki/Fortification Fortification from Wikipedia]
=References=
<references />
'''[[Chess|Up one Level]]'''
[[FILE:Карта-схема к статье «Креста Святого крепость» № 2. Военная энциклопедия Сытина (Санкт-Петербург, 1911-1915).jpg|border|right|thumb| Russian Fortress <ref>A Russian Fortress (1722-1733) at the junction of the rivers Agrakhani and [https://en.wikipedia.org/wiki/Sulak_River Sulak] near the [https://en.wikipedia.org/wiki/Caspian_Sea Caspian Sea] in [https://en.wikipedia.org/wiki/Dagestan Dagestan], at the former western boarder of the [https://en.wikipedia.org/wiki/Tsardom_of_Russia Tsardom of Russia] to [https://en.wikipedia.org/wiki/Iran Persia] of the [https://en.wikipedia.org/wiki/Safavid_dynasty Safavid dynasty], founded by [https://en.wikipedia.org/wiki/Peter_the_Great Peter the Great] while launching the [https://en.wikipedia.org/wiki/Russo-Persian_War_(1722%E2%80%931723) Russo-Persian War], source [https://ru.wikisource.org/wiki/%D0%92%D0%AD/%D0%92%D0%A2/%D0%9A%D1%80%D0%B5%D1%81%D1%82%D0%B0_%D0%A1%D0%B2%D1%8F%D1%82%D0%BE%D0%B3%D0%BE_%D0%BA%D1%80%D0%B5%D0%BF%D0%BE%D1%81%D1%82%D1%8C ВЭ/ВТ/Креста Святого крепость — Викитека] (VE / BT / Cross of the Holy Fortress - Wikisource, [https://www.wikidata.org/wiki/Q4114391 Sytin Military Encyclopedia], [https://en.wikipedia.org/wiki/Saint_Petersburg St. Petersburg], 1911-1915)</ref> ]]
'''Fortress''',<br/>
an [[Endgame|endgame]] drawing technique where a side usually behind in [[Material|material]] sets up a zone of protection that the opponent cannot penetrate <ref>[https://en.wikipedia.org/wiki/Fortress_(chess) Fortress (chess) from Wikipedia]</ref>. While fortresses are quite common in (late) endgames, f.i. in [[Wrong Color Bishop and Rook Pawn]], fortresses may rarely occur in the (late) [[Middlegame|middlegame]], characterized by long fixed [[Pawn Chain|pawn chains]] with up to one or two [[Open File|open files]] but all points of penetration well defended by the weaker side. Chess programs without the implemetation of special knowledge typically fail to recognize fortresses and seem to claim a [[Pawn Advantage, Win Percentage, and Elo|winning advantage]], although they are not able to achieve the win against adequate defence <ref>[[Matej Guid]], [[Ivan Bratko]] ('''2012'''). ''Detecting Fortresses in Chess''. [http://ev.fe.uni-lj.si/ Elektrotehniški vestnik], Vol. 79, Nos. 1-2, [https://ailab.si/matej/doc/Detecting_Fortresses_in_Chess.pdf pdf]</ref>.
=Fortress Detection=
==Evaluation==
Fortress detection might be triggered in [[Evaluation|evaluation]] or [[Interior Node Recognizer|interior node recognizers]] if certain material configurations along with the winning advantage, and [[Pawn Structure|pawn structure]] properties occur. Further [[Pattern Matching|pattern matching]] considering relevant features of fortress positions or fuzzier [[Pattern Recognition|pattern recognition]] is then used to scale the winning advantage towards the [[Score#DrawScore|draw score]] zero - the fuzzier and possibly more error-prone the heuristics, the less the draw scaling. However, due to [[Knowledge#SearchversusKnowledge|search versus knowledge trade-off]], and all that generalization and [[Automated Tuning|tuning]] problems involved with adding knowledge and noise, practical [[Playing Strength|playing strength]] versus usefulness in analysis is an issue.
==Sample==
A pattern of rook vs queen fortress in the endgame was given by [[Lyudmil Tsvetkov]] in his 2017 ''The Secret of Chess'' <ref>[[Lyudmil Tsvetkov]] ('''2017'''). ''[http://www.secretofchess.com/ The Secret of Chess]''. [https://www.amazon.com/Secret-Chess-Lyudmil-Tsvetkov-ebook/dp/B074M85CVV amazon] - Rook vs queen fortress in the endgame, pp. 273</ref>:
One side having just one queen, and at most a single pawn, with the other having just one rook, and at least one pawn, if the queen side has no passers, the rook is protected by a pawn on the g or b files on its 2nd rank, the king of the rook side is adjacent to that pawn, the pawn of the queen side is on files h,f,a or c, and the king of the queen side is not past its 5th rank.
==Search==
Another technique of fortress detection as proposed by [[Matej Guid]] and [[Ivan Bratko]] in 2012 <ref>[[Matej Guid]], [[Ivan Bratko]] ('''2012'''). ''Detecting Fortresses in Chess''. [http://ev.fe.uni-lj.si/ Elektrotehniški vestnik], Vol. 79, Nos. 1-2, [https://ailab.si/matej/doc/Detecting_Fortresses_in_Chess.pdf pdf]</ref> is related to [[Search|search]], in particular [[Iterative Deepening|iterative deepening]] along with "no progress" indication - that is the root evaluation or low search depths already indicate a winning score, which is not increasing in consecutive iterations. A few programs start scaling scores toward zero if the [[Halfmove Clock|halfmove clock]] already exceeds values far below enforcing the [[Fifty-move Rule|50 move rule]], often triggered by conditions mentioned above. Matej Guid and Ivan Bratko further mention the possibility of [[Monte-Carlo Tree Search]] to detect fortresses.
=See also=
* [[Bishops of Opposite Colors]]
* [[Blockade]]
* [[Blockage Detection]]
* [[Draw]]
* [[Draw Evaluation]]
* [[Score#DrawScore|Draw Scores]]
* [[Fortress (Engine)]]
* [[Material#InsufficientMaterial|Insufficient Material]]
* [[Pattern Recognition]]
* [[Check#Perpetual|Perpetual Check]]
* [[Repetitions]]
* [[Stalemate]]
* [[Wrong Color Bishop and Rook Pawn]]
=Selected Publications=
* [[Karsten Müller]], [https://ratings.fide.com/card.phtml?event=4622170 Wolfgang Pajeken] ('''2008'''). ''How to Play Chess Endings''. [https://en.wikipedia.org/wiki/Gambit_Publications Gambit Publications], [https://www.amazon.com/Play-Chess-Endgames-Karsten-Muller/dp/1904600867 amazon], Chapter 11
* [[Lyudmil Tsvetkov]] ('''2010'''). ''Little Chess Evaluation Compendium''. [http://www.winboardengines.de/doc/LittleChessEvaluationCompendium-2010-04-07.pdf 2010 pdf]
* [[Matej Guid]], [[Ivan Bratko]] ('''2012'''). ''Detecting Fortresses in Chess''. [http://ev.fe.uni-lj.si/ Elektrotehniški vestnik], Vol. 79, Nos. 1-2, [https://ailab.si/matej/doc/Detecting_Fortresses_in_Chess.pdf pdf] » [[Rybka]], [[Houdini]] <ref>[http://www.talkchess.com/forum/viewtopic.php?t=64306&start=27 Re: Tony's positional test suite] by [[Louis Zulli]], [[CCC]], August 01, 2017</ref>
* [[Lyudmil Tsvetkov]] ('''2017'''). ''[http://www.secretofchess.com/ The Secret of Chess]''. [https://www.amazon.com/Secret-Chess-Lyudmil-Tsvetkov-ebook/dp/B074M85CVV amazon]
=Forum Posts=
==2000 ...==
* [https://www.stmintz.com/ccc/index.php?id=218993 Thanks -- and a question about "fortress" recognition in programs] by Steve, [[CCC]], March 21, 2002
* [https://www.stmintz.com/ccc/index.php?id=269953 The Bahrain Fortress] by [[Michael Scheidl|Mike Scheidl]], December 10, 2002 » [[Kramnik versus Deep Fritz 2002#6|Kramnik versus Deep Fritz 2002 - Game 6]]
* [https://www.stmintz.com/ccc/index.php?id=378332 missing a win or fortress?] by [[Uri Blass]], [[CCC]], July 21, 2004
==2005 ...==
* [https://www.stmintz.com/ccc/index.php?id=471530 Fortress: is there an engine that can solve this?] by Peter Kasinski, [[CCC]], December 18, 2005
* [http://www.talkchess.com/forum/viewtopic.php?t=13872 Is this positions drawn ?] by M. Ansari, [[CCC]], May 18, 2007
* [http://www.talkchess.com/forum/viewtopic.php?t=23109 Fortress detection program] by Anil, [[CCC]], August 19, 2008
* [http://www.talkchess.com/forum/viewtopic.php?t=28193 Fortress Draws] by [http://www.talkchess.com/forum/profile.php?mode=viewprofile&u=608 Ted Summers], [[CCC]], May 31, 2009
==2010 ...==
* [http://www.talkchess.com/forum/viewtopic.php?t=32034 Funny fortress position] by [[Joona Kiiski]], [[CCC]], January 25, 2010
* [http://www.open-chess.org/viewtopic.php?f=5&t=1015 "No progress" and Graph History Interaction] by [[Mark Watkins|BB+]], [[Computer CHess Forums|OpenChess Forum]], January 23, 2011 » [[Graph History Interaction]]
* [http://www.talkchess.com/forum/viewtopic.php?t=38402 Another fortress position] by Robert Flesher, [[CCC]], March 13, 2011
* [http://www.talkchess.com/forum/viewtopic.php?t=44300 Simple fortress detection, engines fail] by [[Vincent Lejeune]], [[CCC]], July 04, 2012
* [http://www.talkchess.com/forum/viewtopic.php?t=46245 test position: fortress] by [[Jon Dart]], [[CCC]], December 02, 2012
* [http://www.talkchess.com/forum/viewtopic.php?t=47907 Idea for recognizing fortress/encouraging progress] by Piotr Lopusiewicz, [[CCC]], May 03, 2013
* [http://www.talkchess.com/forum/viewtopic.php?topic_view=threads&p=601224&t=54697 Re: Chessprogams with the most chessknowing] by [[Ferdinand Mosca]], [[CCC]], December 20, 2014
==2015 ...==
* [http://www.talkchess.com/forum/viewtopic.php?t=55773 Endgame fortress handling] by [[Lyudmil Tsvetkov]], [[CCC]], March 25, 2015
* [http://www.talkchess.com/forum/viewtopic.php?t=59025 A very subtle fortress destruction] by [[Árpád Rusz]], [[CCC]], January 23, 2016
* [http://www.talkchess.com/forum/viewtopic.php?t=59264 Fortresses] by [[Jon Fredrik Åsvang]], [[CCC]], February 15, 2016
* [http://www.talkchess.com/forum/viewtopic.php?t=62976 Fortresses] by [[Jon Fredrik Åsvang]], [[CCC]], January 30, 2017
* [http://www.talkchess.com/forum/viewtopic.php?t=65247 What does semi-fortress mean?] by [[Jon Fredrik Åsvang]], [[CCC]], September 22, 2017
* [http://www.talkchess.com/forum/viewtopic.php?t=66413 replace the evaluation by playing against yourself] by [[Uri Blass]], [[CCC]], January 25, 2018 » [[Evaluation]]
=External Links=
==On Topic==
* [https://en.wikipedia.org/wiki/Fortress_(chess) Fortress (chess) from Wikipedia]
* [https://chess24.com/en/read/glossary/fortress Fortress - chess term] | [https://en.wikipedia.org/wiki/Chess24.com chess24.com]
* [https://lichess.org/video/SOzdwycf8y0 A Rare Chess Fortress: Queen vs. Bishop & Knight Endgame • Free Chess Videos • lichess.org]
* [https://lichess.org/video/ZsCt9sG6oig? Endgame Fortresses • Free Chess Videos • lichess.org] by [https://en.wikipedia.org/wiki/Varuzhan_Akobian GM Varuzhan Akobian], January 13, 2015
==Misc==
* [https://en.wikipedia.org/wiki/Fortress_chess Fortress chess (variant) from Wikipedia]
* [https://en.wikipedia.org/wiki/Fortification Fortification from Wikipedia]
=References=
<references />
'''[[Chess|Up one Level]]'''
