EVENT
BOARDSIZE 19
SETUP W D16 D10 D4 F4 G4 H3 J3 Q18 O17 L17 
SETUP B G3 H4 H5 K4 K3 Q3 Q5 Q9 Q14 Q16 R17 K15 
MARK 1@K15
COM
Problem 171. White to play.  

Black has played 1. This is not such a good move. How should
White counter it ? 
ENDCOM
W 1 M16
USER
CORRECT ANSWER
ENDUSER
COM
Correct Answer.

Although it may seen strange, White 1 is the correct response.
You might want to make a more aggressive move to erase the black
moyo, but White must be patient. You have to make your base strong
before launching an all-out attack.
ENDCOM
  VAR
  W 1 J16
  COM
  Failure.

  White 1 is a losing move.
  ENDCOM
  B 2 M16
  W 3 M17
  B 4 O16
  MARK 2@M16
  COM
  Black plays 2 and 4 in sente, mapping out a huge moyo in the
  center.
  ENDCOM
  W 5 P17
  MARK A@C17
  COM
  Next, Black can aim at invading the 3-3 point with A, so White's
  territory at the top is not so big. It is clear that White is
  the big loser in this exchange.
  <=
  ENDCOM
  ENDVAR
  VAR
  W 1 L15
  USER
  CORRECT ANSWER
  ENDUSER
  COM
  Correct Answer.

  For reference, let's look at another way White could answer 
  Black's erasure move. Against White 1, ...
  ENDCOM
  B 2 L16
  W 3 M16
  B 4 K16
  MARK 2@L16
  COM
  ... Black responds with 2 and 4.
  ENDCOM
  W 5 K17
  B 6 K13
  W 7 M15
  B 8 H16
  COM
After Black jumps to 8, ...
  ENDCOM
  W 9 M13
  COM
  ... White can also jump to 9. Black's position is not good. However,
  the moves in the Correct Answer are much clearer.
  <=
  ENDCOM
  ENDVAR
B 2 M14
COM
In order to prevent an intrusion into his moyo, Black drops back
to 2.
ENDCOM
  VAR
  B 2 K17
  COM
  Variation.

  If Black attaches at 2, ...
  ENDCOM
  W 3 K18
  B 4 J17
  W 5 J18
  MARK 3@K18
  COM
  ... White plays 3 and 5.
  ENDCOM
  B 6 G17
  COM
  After Black 6, ...
  ENDCOM
  W 7 M14
  COM
  ... White punches a big hole in Black's moyo with 7. It's hard
  to say which side has the more favourable position, but at least
  White has as much chance as Black of winning.
  <=
  ENDCOM
  ENDVAR
W 3 L14
COM
However, because the ladder is favourable for White, 3 is a sever
tesuji.
ENDCOM
B 4 L15
W 5 M15
B 6 M13
COM
Black must extend to 6, but ...
ENDCOM
W 7 L13
B 8 L12
W 9 J14
MARK 7@L13
COM
... then 7 and 9 are powerful moves, challenging Black to a fight
he cannot win.
<=
ENDCOM