Reversi

Reversi/Othello

Players	2
Setup time	5-10 seconds
Playing time	5-60 minutes
Chance	None
Age range	Recommended for 5 years or older
Skills	Strategy, Observation

Reversi (also marketed by Pressman under the trade name Othello) is a board game involving abstract strategy and played by two players on a board with 8 rows and 8 columns and a set of distinct pieces for each side. Pieces typically are disks with a light and a dark face, each side belonging to one player. The player's goal is to have a majority of their colored pieces showing at the end of the game, turning over as many of their opponent's pieces as possible.

Origins

The modern version is based on the game reversi that was invented in 1883 by the Englishman Lewis Waterman, and gained considerable popularity in England at the end of the 19th century. The game is mentioned in an 1895 article in the New York Times: "Reversi is something like Go Bang, and is played with 64 pieces." In 1898, the well-known German games publisher Ravensburger started producing the game as one of its first titles.

The modern rule set, now universally accepted, originated in Mito, Ibaraki, Japan in the 1970s: the Japanese game company Tsukuda Original registered the game under the trademark name Othello. The name was selected as a reference to the Shakespearean play Othello, the Moor of Venice, referencing the conflict between the Moor Othello and Iago, who describes himself as "two faced" and more controversially, to the unfolding drama between Othello, who is black, and Desdemona, who is white. The green colour of the board is insipired by the image of the general Othello, valiantly leading his battle in a green field. It can also be likened to a jealousy competition (jealousy being the central theme in Shakespeare's play), since players engulf the pieces of the opponent, thereby turning them to their possession.

A 2002 press release about the origins of the modern game makes no mention of the original version:

"Othello was invented by Japanese game enthusiast, Goro Hasegawa in 1971. He chose James R. Becker, to help him develop and market the game. Inspired by the ancient Chinese strategy game 'Go', Hasegawa sought to create a game that was rich in strategy, but still approachable by the casual player. Becker simplified the game play, coined the tagline, 'A Minute to Learn...A Lifetime to Master' and named this new game after Shakespeare's classic play, because of the black and white disks. Othello was first introduced in Japan in 1973, by Tsukuda Original Co., who at Becker's suggestion organized the Japanese Othello Association."

Goro Hasegawa, who wrote How to win at Othello, popularized the game in Japan in 1975.

Rules

Each of the two sides corresponds to one player; they are referred to here as light and dark after the sides of Othello pieces, but "heads" and "tails" would identify them equally as well, so long as each marker has sufficiently distinctive sides.

Originally, Reversi did not have a defined starting position. Later it adopted Othello's rules, which state that the game begins with four markers placed in a square in the middle of the grid, two facing light-up, two pieces with the dark side up. The dark player makes the first move.

	a	b	c	d	e	f	g	h
1									1
2									2
3									3
4									4
5									5
6									6
7									7
8									8
	a	b	c	d	e	f	g	h

Starting position

Dark must place a piece with the dark side up on the board, in such a position that there exists at least one straight (horizontal, vertical, or diagonal) occupied line between the new piece and another dark piece, with one or more contiguous light pieces between them. In the below situation, dark has the following options indicated by transparent pieces:

	a	b	c	d	e	f	g	h
1									1
2									2
3									3
4									4
5									5
6									6
7									7
8									8
	a	b	c	d	e	f	g	h

Where dark may play

After placing the piece, dark turns over (flips, captures) all light pieces lying on a straight line between the new piece and any anchoring dark pieces. All reversed pieces now show the dark side, and dark can use them in later moves—unless light has reversed them back in the meantime.

If dark decided to put a piece in the topmost location (all choices are strategically equivalent at this time), one piece gets turned over, so that the board appears thus:

	a	b	c	d	e	f	g	h
1									1
2									2
3									3
4									4
5									5
6									6
7									7
8									8
	a	b	c	d	e	f	g	h

After dark play

Now light plays. This player operates under the same rules, with the roles reversed: light lays down a light piece, causing a dark piece to flip. Possibilities at this time appear thus (indicated by transparent pieces):

	a	b	c	d	e	f	g	h
1									1
2									2
3									3
4									4
5									5
6									6
7									7
8									8
	a	b	c	d	e	f	g	h

Where light may play

Light takes the bottom left option and reverses one piece:

	a	b	c	d	e	f	g	h
1									1
2									2
3									3
4									4
5									5
6									6
7									7
8									8
	a	b	c	d	e	f	g	h

After light play

Players take alternate turns. If one player cannot make a valid move, play passes back to the other player. When neither player can move, the game ends. This occurs when the grid has filled up, or when one player has no more pieces on the board, or when neither player can legally place a piece in any of the remaining squares. The player with the most pieces on the board at the end of the game wins.

Strategy

A beginner often looks for the move that will reverse the greatest possible number of pieces, trying for immediate numerical advantage. For unsophisticated players, this strategy works quite well and will win a majority of games as long as the player thinks at least a few turns in advance. As the experience of the opponent increases, this strategy becomes ineffective. Instead of numerical advantage, the key elements of successful Reversi strategy are corners, mobility, edge play, parity, endgame play and looking ahead.

Corners

Corner positions, once played, remain immune to flipping for the rest of the game (because there is no other opposite color behind them to create a flip); thus a player could use a piece in a corner of the board to anchor groups of pieces (starting with the adjacent edges) permanently. Therefore, capturing a corner often proves an effective strategy when the opportunity arises. More generally, a piece is stable when, along all four axes (horizontal, vertical, and each diagonal), it is on a boundary, in a filled row, or next to a stable piece of the same color. Grabbing a corner prematurely may be a mistake, however, if in doing so the player leaves "holes" along the edge. These holes can be filled by the opposing player and could result in capture of some or all of the pieces along that edge. This renders occupying the corner largely useless.

Mobility

An opponent playing with reasonable strategy will not so easily relinquish the corner or any other good moves. So to achieve these good moves, you must force your opponent to play moves which relinquish those good moves. The best way to achieve this involves reducing the number of moves available to your opponent. If you consistently restrict the number of legal moves your opponent can make, then sooner or later they will have to make an undesirable move. An ideal position involves having all your pieces in the center surrounded by your opponent's pieces. In such situations you can dictate what moves your opponent can make.

When moves seem equal with respect to what moves you will leave yourself and your opponent, playing a minimum piece strategy will tend to give you an advantage, because minimizing your discs will tend to leave fewer discs for your opponent to flip in subsequent moves of the game. One should not play the minimum disc strategy to an extreme, however, as this also can quickly lead to a lack of mobility.

Edges

While playing pieces to edges of the board may seem sound (because they cannot be flipped easily), this strategy can often prove detrimental. Edge pieces can anchor flips that influence moves to all regions of the board. This can poison later moves by causing players to flip too many pieces and open up many moves for the opponent. However, playing on edges where an opponent cannot easily respond drastically reduces possible moves for that opponent.

The square immediately diagonally adjacent to the corner (called the X-square), when played in the early or middle game, typically guarantees the loss of that corner. Nevertheless, such a corner sacrifice is sometimes played for some strategic purpose (like retaining mobility). Playing to the edge squares adjacent to the corner (called the C-squares) can also be dangerous if it gives the opponent powerful forcing moves.

In general, edge play in the early and middle game is to be avoided, unless players can gain larger concessions in terms of mobility or a mass of unflippable pieces.

A good rule of thumb is to keep pieces grouped together in the middle of the board and minimize tangents formed by a player's own pieces. This strategy leads to the greatest mobility.

Parity

Parity is one of the most important parts of the strategy. In short, the concept of parity is about getting the last move in every empty region in the end-game, and thereby increasing the number of stable discs.

The concept of parity led to a change in the perception of the game, as it led to distinct strategies for playing black and white. It forced black to play more aggressive moves and gave white the opportunity to stay calm and focus on keeping the parity. As a result the opening books and mid-game were focused on black being the "attacker" and white being the "defender".

Another side effect of parity is that black should try to complicate the game whereas white should seek to simplify it. It is easier to maintain parity in a simple position.

The concept of parity also controls how edge positions are played and how edges interact.

Endgame

For the endgame (the last 20 or so moves of the game) the strategies will typically change. Special techniques such as sweeping, gaining access, and the details of move-order can have a large impact on the outcome of the game. At these late stages of the game no hard-set rules exist. The experienced player will try to look ahead and get a feel for what will lead to the best final outcome.

Computer opponents

The best Othello computer programs can easily defeat the best humans. As early as 1980, the program The Moor beat the reigning world champion. In 1997, Logistello defeated the human champion Takeshi Murakami in a score of 6:0. By comparison, computers also easily win against the best human players of English draughts (checkers), in chess the best computers are arguably stronger than the best humans, and in Go and Arimaa even average human players can defeat the best computers.

Human beings cannot generally win against the best Othello computer programs, because they can look ahead much further than humans can. Analysts have estimated the number of legal positions in Othello is at most 10²⁸, and it has a game-tree complexity of approximately 10⁵⁸.

Mathematically, Othello still remains unsolved. Experts have not figured out what the outcome of a game will be where both sides have perfect play. However, analysis of thousands of high-quality games (most of them computer-generated) has led to the conclusion that, on the standard 8-by-8 board, perfect play on both sides results in a draw. When generalizing the game to play on an n-by-n board, the problem of determining if the first player has a winning move in a given position is PSPACE-complete. On 4-by-4 and 6-by-6 boards under perfect play, the second player wins.

World Othello Championship

Year	Location	World Champion	Country	Team	Runner-Up	Country
1977	Tokyo	Hiroshi Inoue	Japan	N/A	Thomas Heiberg	Norway
1977*	Monte Carlo	Sylvain Perez	France	N/A	Michel Rengot (Blanchard)	France
1978	New York	Hidenori Maruoka	Japan	N/A	Carol Jacobs	USA
1979	Rome	Hiroshi Inoue	Japan	N/A	Jonathan Cerf	USA
1980	London	Jonathan Cerf	USA	N/A	Takuya Mimura	Japan
1981	Brussels	Hidenori Maruoka	Japan	N/A	Brian Rose	USA
1982	Stockholm	Kunihiko Tanida	Japan	N/A	David Shaman	USA
1983	Paris	Ken'Ichi Ishii	Japan	N/A	Imre Leader	Britain
1984	Melbourne	Paul Ralle	France	N/A	Ryoichi Taniguchi	Japan
1985	Athens	Masaki Takizawa	Japan	N/A	Paolo Ghirardato	Italy
1986	Tokyo	Hideshi Tamenori	Japan	N/A	Paul Ralle	France
1987	Milan	Ken'Ichi Ishii	Japan	USA	Paul Ralle	France
1988	Paris	Hideshi Tamenori	Japan	Britain	Graham Brightwell	Britain
1989	Warsaw	Hideshi Tamenori	Japan	Britain	Graham Brightwell	Britain
1990	Stockholm	Hideshi Tamenori	Japan	France	Didier Piau	France
1991	New York	Shigeru Kaneda	Japan	USA	Paul Ralle	France
1992	Barcelona	Marc Tastet	France	Britain	David Shaman	Britain
1993	London	David Shaman	USA	USA	Emmanuel Caspard	France
1994	Paris	Masaki Takizawa	Japan	France	Karsten Feldborg	Denmark
1995	Melbourne	Hideshi Tamenori	Japan	USA	David Shaman	USA
1996	Tokyo	Takeshi Murakami	Japan	Britain	Stéphane Nicolet	France
1997	Athens	Makoto Suekuni	Japan	Britain	Graham Brightwell	Britain
1998	Barcelona	Takeshi Murakami	Japan	France	Emmanuel Caspard	France
1999	Milan	David Shaman	Netherlands	Japan	Tetsuya Nakajima	Japan
2000	Copenhagen	Takeshi Murakami	Japan	USA	Brian Rose	USA
2001	New York	Brian Rose	USA	USA	Raphael Schreiber	USA
2002	Amsterdam	David Shaman	Netherlands	USA	Ben Seeley	USA
2003	Stockholm	Ben Seeley	USA	Japan	Makoto Suekuni	Japan
2004	London	Ben Seeley	USA	USA	Makoto Suekuni	Japan
2005	Reykjavík	Hideshi Tamenori	Japan	Japan	Kwangwook Lee	South Korea
2006	Mito	Hideshi Tamenori	Japan	Japan	Makoto Suekuni	Singapore
2007	Athens	Kenta Tominaga	Japan	Japan	Stéphane Nicolet	France
2008	Oslo	Michele Borassi	Italy	Japan	Tamaki Miyaoka	Japan
2009	Ghent	Yusuke Takanashi	Japan	Japan	Matthias Berg	Germany

*This rivalling Monte Carlo world championship is usually not considered to be an official world championship. In official homepages it is called the first European Championship.

Further reading

• Ted Landau, Othello: Brief and Basic, An introduction to strategy and tactics for the game of Othello, 1987

External links

• World Othello Federation
• Pressman Othello instructions
• Pictures of the 19th century reversi boards
• Multiplayer Reversi online English, Russian, German.
• "Othello (Reversi)", University of Waterloo, Elliott Avedon Museum & Archive of Games
• Reversi - An Animated Guide
• iOthello: an online international othello community developed for and by Othello players
• Randy Fang, Othello: From Beginner to Master, 2003
• Marc Mandt, Introduction to Basic Othello Strategy and Algorithms, , 2001
• Brian Rose, A minute to learn, life time to master, 2005