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 Geschwentner]]<ref>[https://groups.google.com/d/msg/fishcooking/d8IhZZJSBGc/PrN-8dP26dIJ Followup moves] by [[Stefan Geschwentner]], [[Computer Chess Forums|FishCooking]], January 12, 2014 » [[History Heuristic#CMHist|Counter Moves History]]</ref>, 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.