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=Conditions/Restrictions=
Some programs restrict extensions, with either a maximum limit, or via other conditions, such as depth or iteration. Care must be taken so that the search is not extended infinitely (see [[Search Explosion|search explosion]]). Some programs vary the extension based on the expected [[Node Types|node type]]. For example, in an expected [[Node Types#ALL|All-node]], it might use 1/2 a ply extension for a pawn to the 7th, but a full ply on the [[Node Types#PV|PV-node]] research.
==Non-reductions==
==1996 ...==
* [https://groups.google.com/d/msg/rec.games.chess.computer/1uVIWZFB41k/VUcAUkzyFd0J Fractional depth increments] by S. Read, [[Computer Chess Forums|rgcc]], January 18, 1996
* [https://groups.google.com/d/msg/rec.games.chess.computer/tcjwWnFhXt4/ifkLE7GwfSEJ Crafty V11.3] by [[Robert Hyatt]], [[Computer Chess Forums|rgcc]], October 22, 1996 » [[Crafty]]
* [https://www.stmintz.com/ccc/index.php?id=12201 "Suspicious move" extension] by [[David Eppstein]], [[CCC]], November 20, 1997
* [https://www.stmintz.com/ccc/index.php?id=13993 Extensions?!] by [[Daniel Homan]], [[CCC]], January 13, 1998
* [https://www.stmintz.com/ccc/index.php?id=17954 Move Extensions] by [[Roberto Waldteufel]], [[CCC]], May 04, 1998
* [https://www.stmintz.com/ccc/index.php?id=20167 Extend or not extend in a nullmove tree] by [[Roland Pfister]], [[CCC]], June 08, 1998 » [[Null Move Pruning]]
* [http://www.open-aurec.com/wbforum/viewtopic.php?f=4&t=1754&p=8190 Limiting extensions] by [[David B. Weller]], [[Computer Chess Forums|Winboard Forum]], February 23, 2005 » [[GES]]
* [http://www.open-aurec.com/wbforum/viewtopic.php?f=4&t=4952 Worthless extension ideas...] by [[Mark Lefler|mjlef]], [[Computer Chess Forums|Winboard Forum]], June 06, 2006
* [http://www.talkchess.com/forum/viewtopic.php?t=14594 PVS extension up] by [[Ed Schroder|Ed Schröder]], [[CCC]], June 21, 2007 <ref>[http://www.top-5000.nl/authors/rebel/chess840.htm#PVS Extension Techniques in REBEL (PVS extensions)]</ref> <ref>[http://www.talkchess.com/forum/viewtopic.php?t=15216 @Ed about PV extension] by [[Peter Fendrich]], [[CCC]], Jul 19, 2007</ref>
* [http://www.talkchess.com/forum/viewtopic.php?t=14860 Delaying Extensions Idea (does anyone do this)?] by [[Mark Lefler]], [[CCC]], July 03, 2007
* [http://www.talkchess.com/forum/viewtopic.php?t=20680 Threat extension] by [[Harm Geert Muller]], [[CCC]], April 15, 2008
* [http://www.talkchess.com/forum/viewtopic.php?t=67131 Depth extensions and effect on transposition queries] by [[Kenneth Jones]], [[CCC]], April 16, 2018 » [[Transposition Table]]
* [http://www.talkchess.com/forum3/viewtopic.php?f=7&t=67823 Horizon effect and extensions] by [[Vivien Clauzon]], [[CCC]], June 25, 2018 » [[Horizon Effect]]
* [http://www.talkchess.com/forum3/viewtopic.php?f=7&t=70165 delaying tactics: prune or extend?] by [[Harm Geert Muller]], [[CCC]], March 10, 2019 » [[Selectivity]], [[Tactics]]
=External Links=
* [http://web.archive.org/web/20070607151732/www.brucemo.com/compchess/programming/extensions.htm Search Extension] from [[Bruce Moreland|Bruce Moreland's]] [http://web.archive.org/web/20070607231311/www.brucemo.com/compchess/programming/index.htm Programming Topics]
* [http://www.frayn.net/beowulf/theory.html#extend Computer Chess Programming Theory - Search Extensions] by [[Colin Frayn]]
* [http://www.3dkingdoms.com/chess/implementation.htm Programming Details - Slow Chess | Extensions Used, Detailed Description] by [[Jonathan Kreuzer]] » [[Slow Chess]]
==Misc==
