Chapter 6 · Edge Tactics

Unbalanced Edges (Wings) and How to Attack Them

A shape in which both corners are empty and five discs of the same color run along an edge starting from one C-square is called an unbalanced edge (wing). The C-square on the other side is empty, so it is easy to attack.

If you play the X-square next to the empty C-square of the opponent's wing, you can wedge into that C-square when the opponent takes the nearby corner. The wedged disc has opponent discs on both sides, so it cannot be flipped back, and from this foothold you aim at the corner on the other side as well. This is a corner exchange: you give up one corner to gain a better edge and corner, and usually the side that plays the X-square first gains a tempo. Whether the exchange favors you also depends on the shapes of the other edges and the number of stable discs.

White to move. Black discs run five in a row from A2 to A6, an unbalanced edge, and A7 and A8 are empty. If White plays the X-square B7 next to the empty C-square, the square right next to the C-square is blocked, so Black cannot enter A7. If Black takes A8, White wedges in at A7 and aims at A1 on the other side. Use ▶ to play it (White B7 → Black A8 → White A7).

But a corner exchange does not always work. The examples below show ① to ③ in turn.

  • ① The opponent plays the C-square first: if the opponent plays the C-square first instead of flipping the X-square disc, they take the corner too on their next turn, and the square for your wedge disappears.
  • ② You have no line to the C-square: if you have no line to play the C-square after the opponent takes the corner, you cannot wedge in, and the opponent fills the C-square too.
  • ③ Swindle: if the opponent plays the C-square and takes control of the diagonal connected to the X-square, you cannot take that corner, and the opponent takes it later.
  • An attack that relies on luck: if the opponent cannot enter the C-square only because a distant diagonal happens to consist of your discs alone, the attack is weak, since changing just one disc can block it.
Black to move. White discs run five in a row from H2 to H6, an unbalanced edge. If Black plays the X-square G7, White does not flip G7 but plays the C-square H7 first. On the next turn White takes H8 too, and Black loses the square for the wedge (failure ①). Use ▶ to play it (Black G7 → White H7 → Black C7 → White H8).
White to move. Black discs run five in a row from B8 to F8, an unbalanced edge. If White plays the X-square G7, Black takes H8. Then White has no line to play the C-square G8, so White cannot wedge in (failure ②). Use ▶ to play it (White G7 → Black H8 → White B7).
White to move. Black discs run five in a row from B1 to F1, an unbalanced edge. Even if White plays the X-square G2, once Black plays the C-square G1, White cannot play H1. Black takes that corner later (failure ③, swindle). Use ▶ to play it (White G2 → Black G1 → White F3 → Black H1).

Exercise

Black to move. Find the move that attacks the opponent's five-disc unbalanced edge on the X-square next to its empty C-square.

Exercise

White to move. Find the move that attacks the opponent's five-disc unbalanced edge on the X-square next to its empty C-square.

Exercise

White to move. Find the move that attacks the opponent's five-disc unbalanced edge on the X-square next to its empty C-square.

Exercise

White to move. Find the move that attacks the opponent's five-disc unbalanced edge on the X-square next to its empty C-square.

Exercise

Black to move. Find the move that attacks the opponent's five-disc unbalanced edge on the X-square next to its empty C-square.

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