Type B Strategy

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The Type B Strategy, proposed in 1949 by Claude Shannon in his groundbreaking publication Programming a Computer for Playing Chess, is a selective approach to search minimax trees considering only a subset of plausible moves in contrast to the brute-force Type A strategy.

=Quotes= from Shannon's Programming a Computer for Playing Chess: From these remarks it appears that to improve the speed and strength of play the machine must:

A strategy with these two improvements will be called a type B strategy. It is not difficult to construct programs incorporating these features. For the first we define a function g(P) of a position which determines whether approximate stability exists (no pieces en prise, etc.). A crude definition might be:

| 1 if any piece is attacked by a piece of lower value, g(P) =   /    or by more pieces then defences of if any check exists \   on a square controlled by opponent. | 0 otherwise. Using this function, variations could be explored until g(P)=0, always, however, going at least two moves and never more say, 10.

=Type B programs= Most early chess programs were Type B and used a selective width for a maximum amount of plausible moves to be tried. Bernstein used {7, 7, 7, 7}, later programs chose width dependent from depth, Kotok-McCarthy had {4, 3, 2, 2, 1, 1, 1, 1, 0, 0}, while Greenblatt's Mac Hack used {15, 15, 9, 9, 7, ...}, and CHAOS carried out a selective search with iterative widening. With the advent of brute-force alpha-beta, and programs like Tech, Kaissa and Chess 4.5 in the early 70s, the era of the former dominating Type B programs drew to a close. Today most programs are closer to Type A, but have some characteristics of a Type B due to selectivity.

and
 * Awit
 * Black Knight
 * Blitz
 * CHAOS
 * Chess Simulator
 * Coko
 * Genie
 * Kotok-McCarthy-Program
 * Mac Hack
 * MAX (Gillogly)
 * NSS
 * Schach (US)
 * The Bernstein Chess Program
 * Chess < 4.0

=See also=
 * Alpha-Beta
 * Brute-Force
 * Minimax
 * Selectivity
 * Shannon's Type A Strategy

=Forum Posts=
 * B strategy is the future by Thorsten Czub, CCC, November 04, 2018
 * Which of the many chess engines in this forum use b strategy ? by Thorsten Czub, CCC, October 03, 2020

=External Links=
 * Subject: brute-force vs. intuition in math & chess by Bill Dubuque, August 1996
 * Brute-force search from Wikipedia

=References= Up one Level