How to count liberties

   

It has been suggested that the content of this page should be merged with liberty (tactical sense).



Bill: IMO, that page is too crowded already. Moving some of those examples here would be OK, with a rewrite of the text. :) But to try to merge the two pages would require an extensive rewrite of that page. Besides, linking between pages is the beauty of hypertext. :)

Or I could make this page proprietary, a subpage of my homepage, since the method I describe here is not the textbook treatment.


The English term, liberty, has two meanings. One is an empty point adjacent to a string. Those may be counted by inspection. The other is moves to capture a string. Often the two coincide, but not always. This page gives a basic way to count moves to capture. There are cases where it will not be accurate, but it will work the vast majority of the time.

Suppose that we play a game with these rules. One player, the attacker, makes plays in an attempt to capture a string. The other player, the defender, must pass unless he can make a capture. The attacker's aim is to capture the string in as few net moves as possible; the defender's aim is to save the string or to delay the capture by as many net moves as possible. The number of net moves to capture with optimal play is the liberty count.

[Diagram]

Liberty count for White

In this capturing race White has 4 liberties. After B1 a play at 5 or 7 would allow White to capture. Black plays B3 first, and then can capture in 2 more moves.

[Diagram]

Liberty count for White

This line of play gives the same answer. It would be impractical in a real go game, of course, since White would capture the B3 stone. ;)

[Diagram]

Five-space big eye

White makes 4 plays and then Black captures to prolong the game. The number of net plays so far is 3.

[Diagram]

Five-space big eye (ii)

White makes 3 more plays and then Black captures. The number of net plays so far is 5.

[Diagram]

Five-space big eye (iii)

White makes 3 more plays to capture, for at total number of 8 net plays. (For Black to capture with B4 would not increase the number of net plays.) So the number of liberties for the big eye is 8. That accords with the saying, Five is Eight.


Note that this way of counting liberties is a little funny in this case, because if Black plays first he can live. Similarly, White has 8 liberties by inspection, but White can also live by playing first. However, you can see the utility of this way of counting, because it tells us that whoever goes first can win the capturing race. Mutual life is not optimal.


This is a copy of the living page "How to count liberties" at Sensei's Library.
(OC) 2011 the Authors, published under the OpenContent License V1.0.
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