Anti-Othello

Also called reversed Othello, anti-Reversi or losing Othello. It is the cleanest variant in the family, because it changes exactly one line of the rules and changes almost every judgement you make.

What changes and what does not

One row changes. That is the entire variant.

Why corners turn from gold to poison

In normal Othello a corner is the best square on the board because it can never be flipped. No line runs through a corner from both sides, so once you own it, you own it for the rest of the game. Better still, a corner anchors discs along both edges and the diagonal, and those become permanent too. That is called stability. Stable discs.

Now read that again with the goal reversed. Permanent discs are exactly what you do not want. Taking a corner in anti-Othello hands you a block of discs your opponent can never take back off you, and every one of them counts against you at the end.

A position where the engine turns a corner down

Here is the same position handed to the same engine twice, once under normal rules and once under anti rules. Black has 24 discs and white has 31, white is to move, and there are 4 legal moves: h1, b2, g8, h8. With 9 squares empty, the engine solves the position exactly rather than estimating, so both answers below are proved.

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Under normal rules the engine plays h1, the corner, without hesitating. Under anti rules it plays b2 and leaves the corner sitting there. Both answers come out of the same search code with one flag changed, and at this stage of the game both are proofs rather than opinions.

Notice which square the anti engine reaches for. In the normal game b2 is an X-square, one of the four most dangerous squares on the board. Here it is a sensible move, because giving your opponent a corner is a way of making them hold the permanent discs. X-squares and C-squares.

What still holds

Not everything inverts, and the parts that survive are the parts worth learning.

• Mobility. Having legal moves is good in both games. A player with nothing to play has to pass while the opponent shapes the board to suit themselves, and that hurts whichever way you count at the end. Mobility.
• Parity. Who gets the last move in a region still matters, because the last move in a region is unanswerable. The player it favours changes, the idea does not. Parity.
• Quiet moves. Flipping as few discs as possible on each move is good advice in normal Othello and even better advice here.
• Wipeouts still end the game. If you lose every disc, the game stops immediately, and in anti-Othello that means you win outright with zero discs. Chasing it deliberately is usually a mistake, since your opponent controls whether it happens.

How the engine handles the variant

In the library behind this site, the anti variant is a single flag on the game state. Move generation, flipping and passing are untouched, because none of them depend on who is winning. Two things change:

• The evaluation is negated, so a position that scores well for you in the normal game scores badly here.
• A pruning shortcut is switched off. The normal search can skip a branch early when the opponent already holds enough unflippable discs to cap your best possible margin. That reasoning depends on more discs being better, so it would be wrong in anti-Othello and is disabled.

As a sanity check, the engine was set to play itself under anti rules at its Hard level. The game finished 43 discs to 21, and the side with 21 won. In a normal game that would be a heavy defeat.

How to play it

Agree the rule before the first move, out loud, because "fewest discs wins" sounds like a joke until someone loses on it. Then set up and play exactly as normal. The board on this site plays the standard game, so use a physical set, or the two player board here and count the other way round when you finish.

Play it once against someone who is much better than you at normal Othello. Experience is a handicap in anti-Othello for about twenty minutes, which is the most entertaining twenty minutes the variant has to offer.

Where to go next

All Reversi variants covers small boards, 10x10 boards and four player Rolit. The strategy guide explains the normal principles this variant inverts, and how the engine works explains the search that produced the position above.