Reversi (Othello) — Strategy
VOG — Vinco Online Games
Stoner traps
We just saw that attacking an unbalanced edge does not force the exchange of corners. Indeed, the attacked player can decide whether to take the corner or not. We will now see a more forcing edge trap which leads to a guaranteed corner. As with the unbalanced edge attack, the Stoner trap provokes a corner exchange but this time, if the trap is well executed, the defender has no means to prevent it.
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The Stoner trap proceeds in two stages: the attacker first gains control of a diagonal by playing to an X-square, then he attacks the opponent's weak edge (an edge including a C-square) while threatening to take the corner. The opponent cannot respond by taking back the edge since in this case he would flip back the X-square played the previous move. Diag. 36 gives an example. Here, black has a weak edge configuration on the south. White plays b7 and takes control of the e4-b7 diagonal (see Diag. 37). Black can't immediately take the a8 corner, and he will probably try to retake the diagonal to gain access to this corner, for example by playing f3. But now, white plays his attacking move d8 (see Diag. 38). Black cannot prevent white from having the h8 corner and at least six stable discs on the south edge. If black responds with b8, he flips the b7 disc, thus giving up the a8 and subsequently h8 corners to white. If black takes the a8 corner, white can directly take the h8 corner or, better yet, wedge in with b8, keeping access to h8. Furthermore, even if black plays neither a8 nor b8, white always has access to h8 (this being the difference between an unbalanced edge attack). As in the case of unbalanced edges, the trap isn't always possible and it's necessary to be careful in checking that the sequence of moves is correct. Here is an example, in Diag. 39, of a Stoner trap which doesn't work. If white wants to play a Stoner trap by playing b7, black responds c3 and white can no longer play c8 before black takes the a8 corner. The south edge now consists only of a pair of empty squares and white cannot wedge in. |
