Changes

A combination of the History Heuristic in conjunction with the [[Countermove Heuristic]], proposed by [[Bill Henry]] in March 2015 <ref>[http://www.talkchess.com/forum/viewtopic.php?t=55535 Improving History Tables] by [[Bill Henry]], [[CCC]], March 02, 2015</ref> , as already used by [[Álvaro Begué]] in his [[Checkers]] program 20 years before <ref>[http://www.talkchess.com/forum/viewtopic.php?t=55535&start=2 Re: Improving History Tables] by [[Álvaro Begué]], [[CCC]], March 02, 2015</ref> , was implemented by [[Stockfish]] contributor [[Stefan Geschwenter]], further tuned and improved by the Stockfish community, and released in [[Stockfish|Stockfish 7]] in January 2016, dubbed '''Counter Moves History''' and mentioned to gain some Elo points <ref>[http://www.talkchess.com/forum/viewtopic.php?t=58935&start=2 Re: Stockfish 7 progress] by Lucas Braesch, [[CCC]], January 17, 2016</ref> . Stockfish's History and Countermove arrays are piece type and [[Target Square|to-square]] based, not butterfly based. Each entry indexed by a previous move, is a complete history table with counters indexed by the move refuting that previous move. Pushing the idea further, Stockfish applies '''Follow Up History''' (FUH) tables, indexed by two consecutive moves of the same side <ref>[http://www.talkchess.com/forum3/viewtopic.php?f=7&t=72531&start=1 Re: CMH question] by Lucas Braesch, [[CCC]], December 09, 2019</ref>.