Reductions

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Reductions (as opposed to pruning), a class of search heuristics that decrease the depth to which a certain branch of the tree is searched, also interpreted as negative extension.

=Recursive Reductions=
 * Late Move Reductions - LMR
 * Fail-High Reductions - FHR
 * Null Move Reductions

=Near the Tips=
 * Razoring

=Pruning after a reduced Search= Some dynamic pruning techniques base their pruning decision on a reduced search by factor R, also applied recursively:
 * Null Move Pruning
 * Multi-Cut

A none recursive pruning based on reduction at some fixed depth is applied by:
 * ProbCut

=See also=
 * Pruning
 * Extensions

=Forum Posts=

1998 ...

 * A new selective heuristic? by Frank Schneider, CCC, June 21, 1998

2000 ...

 * Evaluation-based Reductions and/or Extensions by Tom Likens, CCC, December 28, 2003 » Extensions
 * extensions + reductions + pruning = confusion by Johan de Koning, CCC, March 24, 2004 (was Shredder 8 secret: search depth?)

2005 ...

 * Reductions and null move refutations by Tord Romstad, Winboard Forum, April 18, 2005 » Null Move Pruning
 * Has anyone tested Gambit Fruit with Rebel Reductions on? by Ryan B., CCC, November 15, 2005 » Rebel, Gambit Fruit
 * Reducing King Moves? by mjlef, Winboard Forum, January 03, 2007
 * Toga/Glaurung/Strelka Prunings/Reductions by Edsel Apostol, CCC, January 31, 2008 » Toga, Glaurung, Strelka, Pruning

2010 ...

 * Reducing/Pruning Bad Captures (SEE < 0) by Edsel Apostol, CCC, August 19, 2011 » SEE
 * Reductions from internal iterative deepening by Evert Glebbeek, CCC, August 20, 2012 » Internal Iterative Deepening
 * Houdini 3 reducing the depth feature by Maurizio Maglio, CCC, October 17, 2012 » Houdini
 * Pruning in PV nodes by Sergei S. Markoff, CCC, January 14, 2014 » Root, Node Types
 * variable reductions by Robert Hyatt, CCC, June 22, 2014

2015 ...

 * Ratio reduction by Steven Edwards, CCC, September 20, 2015 » Late Move Reductions, Symbolic
 * Reduction Research Question by Dennis Sceviour, CCC, September 25, 2015
 * Reductions by Harm Geert Muller, CCC, May 22, 2016
 * EMR & EMP by Michael Sherwin, CCC, July 19, 2016
 * Floating Move Reduction by Dennis Sceviour, CCC, September 14, 2016
 * EMR based on Null Move threat by Michael Sherwin, CCC, October 30, 2017

=External Links=
 * Reduction from Wikipedia
 * Programmer Corner - How Rebel Plays Chess - Reductions by Ed Schröder, pdf reprint

=References=

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