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Clamp
Keywords: Shape
Black 1 here is known as the clamp. Notice that it applies pressure on the two white stones.
TakeNGive: Is this Black 1 also the clamp? (If White blocks at a, Black connects at b, and vice-versa.) Or is this called something else? Also, this seems to work only on the second line, I guess because the edge of the board is close.
This is Takagi Shoichi (Black) versus Kato Masao in the 43rd Honinbo League played in November 1987. Takagi uses it as the first example in section 2 of Beyond Forcing Moves?. When White plays at 2, Black continues at 3 and 5 in the knowledge that the clamp at 7 is available. However, the point of including it in his book is as an example of good forcing moves - by White! The clamp is effective in that White cannot prevent Black from connecting. However, Takagi did not really consider how well White could do by using a sacrifice strategy. He may not have known that thirteen years earlier (December 1974) Sakata Eio had beaten Kato in the 30th Honinbo League with the same sacrifice in the same corner position. (Thank you GoGoD CD and Kombilo :-)
White's turn at 3 yields a free forcing move in the corner at 5 before continuing with 7 and then stopping Black cold with 9.
Finally White ends the play in the upper right in sente with 1 and turns to 3 to expand the upper left territory now backed up by White's new wall in the upper side.
Note that White can not win by turning at 3 after exchanging 1 for 2. Black 4, 6, and 8 make miai of a and b.
See also: This is a copy of the living page "Clamp" at Sensei's Library. (C) the Authors, published under the OpenContent License V1.0. |