Nets and ladders - what might they have in common? If your guess is that it's something related to stockings, then (how can I put this?) you may not have soaked up enough of the Go-playing ambience to be completely saturated.
Ladders and nets are fundamental tactics for capturing stones. Ladders are representative of "chase and destroy" methods, while nets will give us a start on "surround and suffocate", the very basic thought that one can attack by first shutting in the opponent's stones.
There is a game in progress that promises some fireworks: GOLD is playing YOUNG, one of his strong friends. Here's the position that greets us.
White (YOUNG) has shut in four black stones (triangled) on the top side, but only loosely. Black (GOLD) plays 1 as shown to get some tactical leverage against the blockading white stones. White replies resolutely with 2. What will happen?
Black can cut off and capture a single White stone in this way. White cannot save it (right-hand diagram). But that's small potatoes. Black loses the four stones he set out to rescue.
Black must continue this way, splitting White's outside stones into three separate chains. So far so good. But now Black is committed to capturing some of those white stones. Otherwise Black's inside stones have no chance of survival.
One possibility that must be considered is the ladder tactic. Black starts it off with 9 and 11 here, and establishes the pattern with 13, 15 and so on. The black stones are placed to block White's natural line of advance. Each of Black's plays is a threat to capture, forcing White to answer as shown. If the situation were as straightforward as in the right-hand diagram, this attack would be decisive. When the diagonal development of the ladder hits the edge of the board, all the white stones are lost.
However, that is not the case here. Black must beware of playing blindly on in the ladder, without regard to the possible hazards. Suppose this position is reached - it would be Black's turn, but White has effectively connected the central chain to one already there in the lower left. What can Black do? The attack cannot be sustained, and the Black weaknesses marked 'C' are very grave. At each one of them White threatens to do as in the right-hand diagram: play a double threat to capture (double atari). This would be a quick way for Black to lose the game. As Go players say, the ladder is broken; and no good will come of applying it.
Since the players involved are highly skilled, Black does have another resource. Black 9 here ties up the two key White stones in a net - it relies on the exchange Black A, White B, which is forcing for Black. The middle diagram makes this explicit, for clarity showing that exchange already made: if White pushes out at 1 Black's answer at 2 keeps the white stones netted. The right-hand diagram shows two of the simplest types of net (which are many and various); the triangled stones in them are lost.
First published 16 March 2000 as On Your Side on MindZine,
© Charles Matthews 2000.