Winning a capturing race  

Impossibility to approach a stone at the 1-2 point from the corner 1-1 point. This can give the player who occupies the 1-2 point an additional tempo to win a capturing race. The double shortage of liberties situation illustrates this case.

Efficient eye making

Eye in corner  

Occupying both 1-2 points is the most efficient way of making an eye, provided that the 2-2 point cannot be occupied by the opponent. This aspect is a recurring theme in many corner life-and-death problems.

Ko in the corner

Ko in corner  

A ko in the corner only needs five stones.

Bent four in the corner  

The 1-2 point can often be used to force a ko in the corner at the 1-1 point, such as the bent four in the corner as shown in this diagram. This has ramifications in both capturing races and life-and-death situations. A couple of endgame tesujis also rely on this peculiarity.

Throw-in

Throw in at 1-2  

threatens to capture with the throw-in at the 1-2 point, because of the weakness at a.

Efficient consumption of liberties

A play at a 1-2 point removes half the liberties of 1-1 while having two other liberties; this is more efficient in this respect than any other play. If we define the efficiency of a point x with respect to a neighbour y as liberties of x / liberties of y – which is the same as (fraction of liberties of y occupied by x) / (fraction of liberties of x occupied by y) – we have the following efficiencies:

• Edge:corner (1-2 : 1-1) ⇒ 1½
• Middle:edge ⇒ 1⅓
• Edge:edge , middle:middle ⇒ 1

Examples

Approach moves

Usual way to fight a capturing race  

If White just starts to fill Black’s liberties, Black wins.

Take the 1-2 point first  

But if she starts with at 1-2, White wins.

Here Black cannot attack from either side because of shortage of liberties.

Throw-in

Some examples of throw-in tesujis at the 1-2 point are shown in Stupid Moves numbers 1 and 2; here is another:

White 2 was a small mistake  

Black played as a ko-threat. I will not discuss whether this was the best threat. White answered at giving Black another threat at a. White should have played at a.

A direct atari  

Here was in answer to , which it also directly threatens.

The throw-in , at the 1-2 point, captures , because of the weakness at a.

Actually, I can point to a stupid player with White who lost a ko because of this very mistake. It was a certain HolIgor (IGS 5k*).

Kos

The 1-2 point is a place where many kos happen. For example, the ko that HolIgor (IGS 5k*) lost.

Black starts ko  

Black plays hoping for White’s mistake. White sees the ko. White suspects that she wins the capturing race without ko (but it is so difficult to read 8 moves ahead, shame on her!), and she decides to fight the ko.

But the sad story of White’s mistake has little to do with the topic of this page, the 1-2 point. By taking it, Black got a ko that saved his group.

White makes life  

or

Guess there’s a disadvantageous ko here...  

-- Malweth

Problem 1  

/Problem 1 Attempts
/Problem 1 Solution?

Problem 2  

/Problem 2 Attempts
/Problem 2 Solution?

Problem 3  

/Problem 3 Attempts
/Problem 3 Solution?

Problem 4  

/Problem 4 Attempts
/Problem 4 Solution?

Problem 5  

/Problem 5 Attempts?
/Problem 5 Solution?

Problem 6  

/Problem 6 Attempts
/Problem 6 Solution?

Problems on other pages

• Xuanxuan Qijing Unnumbered Problem 2
• RTG Problem 84
• Gokyo Shumyo, Section 1, Problem 2
• Endgame Problem 7
• 1-2 point - fun problem