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Key collisions or type-1 errors are inherent in using signatures with far less bits than required to encode all reachable chess positions. A key collision occurs when two different positions map the same hash key or signature <ref>[http://www.talkchess.com/forum/viewtopic.php?t=40062 TT Key Collisions, Workarounds?] by [[Clemens Pruell]], [[CCC]], August 16, 2011</ref> <ref>[http://www.talkchess.com/forum/viewtopic.php?t=44082 how to measure frequency of hash collisions] by [[Daniel Shawul]], [[CCC]], June 16, 2012</ref> . When storing only a partial key, the chance of a collision greatly increases. To accept only hits where [[Hash Move|stored moves]] are [[Pseudo-Legal Move|pseudo-legal]] decreases the chance of type-1 errors. On his computer chess page <ref>[http://www.cse.buffalo.edu/~regan/chess/computer/ Computer Chess - Hash Collisions in Chess Engines, and What They May Mean...] by [[Kenneth Wingate W. Regan]]</ref>, [[Kenneth Wingate W. Regan|Ken Regan]] broached on chess engine bugs, anomalies and hash collisions, and mentions a [[Shredder|Shredder 9.1]] game where a key collision might have caused a strange move <ref>[http://www.chessgames.com/perl/chessgame?gid=1352348 Pablo Lafuente vs Shredder (Computer) (2005)] from [http://www.chessgames.com/index.html chessgames.com]</ref> <ref>[http://www.chessbase.com/newsdetail.asp?newsid=2525 Current tournaments – Sanjin, Biel, Argentina, Israel], [[ChessBase|ChessBase News]], July 21, 2005</ref> .

* [http://www.talkchess.com/forum/viewtopic.php?t=66640 Marcel Duchamp endgame "splits" engines / hash phenomenon] by [[Kenneth Wingate W. Regan|Kenneth Regan]], [[CCC]], February 19, 2018 » [[:Category:Marcel Duchamp|Marcel Duchamp]]

* [http://www.cse.buffalo.edu/~regan/chess/computer/ Computer Chess - Hash Collisions in Chess Engines, and What They May Mean...] by [[Kenneth Wingate W. Regan]]