Reversi (Othello) — Strategy
VOG — Vinco Online Games
Unbalanced edges
We are now going to examine a very frequent case of wedging. This example is equally important since as we shall see it isn't always a bad idea to play to an X-square. Consider Diag. 32.
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The game is now nearly complete, but neither of the two players has succeeded in gaining a clear win, and black must now play. Whatever he does, he must give up a corner to white. Look closely at what's happening on the east edge. The structure of 5 white discs on the h column is called an unbalanced edge. It's a weakness since it often permits your opponent to sacrifice the corner. Let's look at the details with an example. If black plays to the X-square g2, white could respond by taking the corner, h1; but then black can wedge in with h2 (see Diag. 33). The h1 corner allows white to stabilize the north edge: he has 7 stable discs. However, black's wedge at h2 allows him to play h8 (a corner !) on his next move then a8 (another corner !). He has amassed 14 stable discs, with most likely the western edge to come; furthermore, he still has a move to g7: the exchange of corners is very favourable to black. The unbalanced edge of white on the east edge makes a black move of g2 very favourable indeed in Diag. 32. |
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In fact, in practise the situation is a bit more complicated: white is not forced to take the corner. This move leads to a possible exchange of corners. Each player must determine if this exchange is favourable to them or not: everything will depend on the other edges and the number of stable discs which each player stands to gain. However, in general, this move allows one of the players to gain a tempo by playing to the appropriate X-square. One should not believe that this sacrifice works every time. Without entering into details, here are three examples of sacrifices which do not work. |
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In Diag. 34, white has two unbalanced edges: to the north and to the west. However, neither of these two is attackable. If black plays b2, white plays b1 (without flipping b2), then plays a1 on his next move, without giving black the chance to wedge. If black plays b7, white plays a8 and black cannot wedge in at a7; white will play there himself on the next move. The position in Diag. 35 is a bit more subtle: what will happen if black attacks the white west edge by playing b7? White will respond then with a7 (!), controling the f3-b7 diagonal, so black cannot take the a8 corner and white can play there next move thanks to his wedge at d8. Here again, black has failed at his attempted wedge. |
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The situation above is referred to as a swindle. This term is easily understood: the usual sequence of moves on the west edge doesn't work due to white's control of the diagonal. There are other examples of swindles and you must always be very careful to check if your opponent can play an unforseen sequence of moves which will ruin your corner sacrifice. |
