Editing Reversi (section)

== Computer opponents and research ==
{{main|Computer Othello}}

Good [[Computer Othello|Othello computer programs]] play very strongly against human opponents. This is mostly due to difficulties in human look-ahead peculiar to Othello: The interchangeability of the disks and therefore apparent strategic meaninglessness (as opposed to [[chess]] pieces for example) makes an evaluation of different moves much harder. This can be demonstrated with blindfold games, as the memorization of the board demands much more dedication from the players than in [[blindfold chess]].

The first tournament pitting ''Othello'' computer programs against human opponents took place in 1980. In it, then world champion Hiroshi Inoue, although he would go on to win the tournament, lost a game against the computer program ''The Moor''. In 1997, the computer ''Othello'' program [[Logistello]] defeated the reigning human champion, [[Takeshi Murakami]], six games to zero.<ref>{{Cite book |last=Buro |first=Michael |title=Entertainment Computing |year=2003 |isbn=978-1-4757-5153-6 |series=IFIP Advances in Information and Communication Technology |volume=112 |pages=81–88 |chapter=The Evolution of Strong Othello Programs |doi=10.1007/978-0-387-35660-0_10}}</ref>

Analysts have estimated the number of legal positions in ''Othello'' is at most 10<sup>28</sup>, and it has a [[game-tree complexity]] of approximately 10<sup>58</sup>.<ref name="Allis1994">{{Cite book |last=Allis |first=Victor |url=http://fragrieu.free.fr/SearchingForSolutions.pdf |title=Searching for Solutions in Games and Artificial Intelligence |publisher=PhD Thesis, University of Limburg, Maastricht, The Netherlands |year=1994 |isbn=90-900748-8-0 |author-link=Victor Allis |archive-url=https://web.archive.org/web/20050307024938/http://fragrieu.free.fr/SearchingForSolutions.pdf |archive-date=7 March 2005 |url-status=live}}</ref> Mathematically, Othello is solved up to 8x8 board. On 4×4 and 6×6 boards under perfect play, the second player wins.<ref>{{Cite web |title=Amenor |url=http://www.feinst.demon.co.uk/Othello/Jul93/Amenor.html |archive-url=https://web.archive.org/web/20131029222549/http://www.feinst.demon.co.uk/Othello/Jul93/Amenor.html |archive-date=29 October 2013}}</ref> On 8x8 board, the game results in draw under perfect play, according to an [[arXiv]] paper.<ref>{{Cite arXiv |title=Othello is Solved |eprint=2310.19387 |last1=Takizawa |first1=Hiroki |date=2023 |class=cs.AI }}</ref> The first of these [[Mathematical proof|proof]]s is relatively [[Triviality (mathematics)|trivial]], the second dates to around 1990, and the last one was done in 2023. When [[generalized game|generalizing]] the game to play on an ''n''×''n'' board, the problem of determining if the first player has a winning move in a given position is [[PSPACE-complete]].<ref>{{Cite journal |last1=Iwata |first1=S. |last2=Kasai |first2=T. |year=1994 |title=The Othello game on an n*n board is PSPACE-complete |journal=Theor. Comput. Sci. |volume=123 |issue=2 |pages=329–340 |doi=10.1016/0304-3975(94)90131-7}}</ref>