Life In 19x19

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[go]$$Bc Is it alive?
$$ | . . . . . .
$$ | . O . . . .
$$ | O . . . . .
$$ | X O O . O .
$$ | X X X O . .
$$ | . . X O . .
$$ | O . X O O .
$$ | O X X X O .
$$ | . O . X O .
$$ +-------------[/go]

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[go]$$Wc
$$ | . . . . . .
$$ | . O . . . .
$$ | O . . . . .
$$ | X O O . O .
$$ | X X X O . .
$$ | . . X O . .
$$ | O . X O O .
$$ | O X X X O .
$$ | . O 1 X O .
$$ +-------------[/go]

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[go]$$Wc
$$ | . . . . . .
$$ | . O . . . .
$$ | O . . . . .
$$ | X O O . O .
$$ | X X X O . .
$$ | . . X O . .
$$ | O . X O O .
$$ | O X X X O .
$$ | 2 . . X O .
$$ +-------------[/go]

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[go]$$Wc
$$ | . . . . . .
$$ | . O . . . .
$$ | O . . . . .
$$ | X O O . O .
$$ | X X X O . .
$$ | . . X O . .
$$ | O . X O O .
$$ | O X X X O .
$$ | . 3 . X O .
$$ +-------------[/go]

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[go]$$Bc
$$ | . . . . . . . .
$$ | . . . O . . . .
$$ | . . . . X . . .
$$ | . . O . . . . .
$$ | . . . 4 . X . .
$$ | . . 3 O . . . .
$$ | . . 1 2 8 X . .
$$ | . . 7 5 6 9 . .
$$ | . . . . . 0 . .
$$ +-------------[/go]

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[go]$$Bcm11
$$ | . . . . . . . .
$$ | . 6 . O . . . .
$$ | 4 . . . X . . .
$$ | 3 2 O . . . . .
$$ | 5 1 . O . X . .
$$ | . . X O . . . .
$$ | . . X O O X . .
$$ | 0 . X X O X . 9
$$ | . . . . 8 O 7 .
$$ +-------------[/go]

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[go]$$Bcm21
$$ | . . . . . . . .
$$ | . O . . . . . .
$$ | O . . . X . . .
$$ | X O O . 4 . . .
$$ | X X 3 O . X . .
$$ | . . X O . . . .
$$ | 6 . X O O X . .
$$ | O 5 X X O X . X
$$ | . 2 . 1 O O X .
$$ +-------------[/go]

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[go]$$Bcm11
$$ | . . . . . . . .
$$ | . O . O . . . .
$$ | O . . . X . . .
$$ | X O O . . . . .
$$ | X X . O . X . .
$$ | . . X O . . . .
$$ | . . X O O X . .
$$ | . . X X O X . 9
$$ | . . . 7 8 O . .
$$ +-------------[/go]

We decided we were playing with AGA rules, so that if Black's 4th move was to pass (and use a passing stone), then this 4 move cycle would not affect the score. So it seems that if White wants to, she can keep playing this cycle infinitely and so it's sort of like triple ko and thus a draw.

AGA rules: those include a superko rule. So the cycle cannot be repeated without ko threats being played elsewhere. Games played by AGA rules are never a draw, they always have an outcome. If you are unsure about life and death, you should solve it by removing all dead groups (both players) by play after the first two passes. Any groups the opponent is unable to remove are alive.

Japanese rules used in the west: those say that if a position repeats and both players agree, then the game is a draw. As for disputes, you should find the optimal sequence using a slightly modified ko rule (ko can only be retaken after passing), and see where it leads.

Click Here To Show Diagram Code

[go]$$Bc Is it alive?
$$ | . . . . . .
$$ | . O . . . .
$$ | O . . . . .
$$ | X O O . O .
$$ | X X X O . .
$$ | . . X O . .
$$ | O . X O O .
$$ | O X X X O .
$$ | . O 1 X O .
$$ +-------------[/go]

Bill Spight wrote:See http://senseis.xmp.net/?SendingTwoReturningOne

Different rules handle Sending Two, Returning One in different ways. But in all of them there is no endless repetition when there is a single one of them on the board.

Bill Spight wrote:In this case,

$$Bc Is it alive?
$$ | . . . . . .
$$ | . O . . . .
$$ | O . . . . .
$$ | X O O . O .
$$ | X X X O . .
$$ | . . X O . .
$$ | O . X O O .
$$ | O X X X O .
$$ | . O 1 X O .
$$ +-------------

Click Here To Show Diagram Code

[go]$$Bc Is it alive?
$$ | . . . . . .
$$ | . O . . . .
$$ | O . . . . .
$$ | X O O . O .
$$ | X X X O . .
$$ | . . X O . .
$$ | O . X O O .
$$ | O X X X O .
$$ | . O 1 X O .
$$ +-------------[/go]

Black can make a ko. Whether that is a good idea or not is another question.

tiger314 wrote:AGA rules: those include a superko rule. So the cycle cannot be repeated without ko threats being played elsewhere. Games played by AGA rules are never a draw, they always have an outcome. If you are unsure about life and death, you should solve it by removing all dead groups (both players) by play after the first two passes. Any groups the opponent is unable to remove are alive.

Shawn Ligocki wrote:

Bill Spight wrote:See http://senseis.xmp.net/?SendingTwoReturningOne

Different rules handle Sending Two, Returning One in different ways. But in all of them there is no endless repetition when there is a single one of them on the board.

Thanks, that article clarifies things.

Bill Spight wrote:In this case,

$$Bc Is it alive?
$$ | . . . . . .
$$ | . O . . . .
$$ | O . . . . .
$$ | X O O . O .
$$ | X X X O . .
$$ | . . X O . .
$$ | O . X O O .
$$ | O X X X O .
$$ | . O 1 X O .
$$ +-------------

Click Here To Show Diagram Code

[go]$$Bc Is it alive?
$$ | . . . . . .
$$ | . O . . . .
$$ | O . . . . .
$$ | X O O . O .
$$ | X X X O . .
$$ | . . X O . .
$$ | O . X O O .
$$ | O X X X O .
$$ | . O 1 X O .
$$ +-------------[/go]

Black can make a ko. Whether that is a good idea or not is another question.

Thanks, but I have to do that before white fills in two liberties, so can't necessarily fix all my ko threats first. Tricky situation.

Shawn Ligocki wrote:

tiger314 wrote:AGA rules: those include a superko rule. So the cycle cannot be repeated without ko threats being played elsewhere. Games played by AGA rules are never a draw, they always have an outcome. If you are unsure about life and death, you should solve it by removing all dead groups (both players) by play after the first two passes. Any groups the opponent is unable to remove are alive.

Oops, thanks for the clarification. I didn't know AGA had superko. So, my understanding of this case is that White will eventually fill two black liberties on the left and then repeatedly cycle the loop.

Black cannot pass because that would repeat a board position, so black must play elsewhere instead and eventually Black will run out of places to play and there will be no legal moves for him except filling his own eyes somewhere?

So instead, Black must play ko before white has filled 2 liberties? But the ko is also looks complicated, because it's sort of a two stage ko? Maybe Ten Thousand Year Ko?

Bill Spight wrote:

Shawn Ligocki wrote:Black cannot pass because that would repeat a board position, so black must play elsewhere instead and eventually Black will run out of places to play and there will be no legal moves for him except filling his own eyes somewhere?

No, the AGA Superko rule allows repetition by a pass. With exceptions so rare that they have never been known to occur in actual play, the AGA Superko rule will prevent a board play by White, not Black.

6) Repeated Board Position (Ko): It is illegal to play in such a way as to recreate a
previous board position from the game, with the same player to play.
{The most typical example is a situation where the players can each alternately capture
and recapture a single stone. This is known as "ko" (See Figure 3). After the first
capture, the player moving next may not capture immediately, as this would repeat the
board position; instead, that player must play elsewhere on the board (or pass). The
player who first captured may then "fill" the ko (or otherwise resolve it), or play
elsewhere as well (often in response to the other player's previous move.) If the board
position has changed, and the ko has not yet been resolved, the opponent is then free
to capture, and it is the original player who may not then immediately recapture. This
process is known as a ko fight, and the moves played away from the ko itself are known
as ko threats.
Figure 3. Ko
Rarely, multiple kos or other repetitive situations will arise; the principle for handling
them is always the same: the players must avoid repeating the full-board position, so
they are periodically, and alternately, forced to play away from the repetitive situation
before responding.}

8) Illegal Moves: An illegal move is one violating the rules. If a player makes an
illegal move--such as moving twice in a row (i.e., before the opponent has made a
response), attempting to play on an occupied intersection, self-capture, or
retaking a ko so as to repeat the full board position, the player must take back his
or her move (both moves, if he or she moved twice in succession), it shall be
treated as a pass, and a pass stone exchanged.
An illegal move must be noted as such by the opponent before he or she makes
his or her move. When a player moves, he or she is tacitly accepting the
opponent's previous move as valid. In particular, if it is discovered that an earlier
move by one of the players was illegal, the game must nevertheless be continued
as it stands unless both players agree to restore the earlier board position and
proceed from that point.

Certain moves are illegal (Rules 5 and 6), but a pass is always legal (Rule 7).

Shawn Ligocki wrote:

Bill Spight wrote:

Shawn Ligocki wrote:Black cannot pass because that would repeat a board position, so black must play elsewhere instead and eventually Black will run out of places to play and there will be no legal moves for him except filling his own eyes somewhere?

No, the AGA Superko rule allows repetition by a pass. With exceptions so rare that they have never been known to occur in actual play, the AGA Superko rule will prevent a board play by White, not Black.

Oh my this is confusing, looking at http://www.usgo.org/files/pdf/completerules.pdf I see:

6) Repeated Board Position (Ko): It is illegal to play in such a way as to recreate a
previous board position from the game, with the same player to play.
{The most typical example is a situation where the players can each alternately capture
and recapture a single stone. This is known as "ko" (See Figure 3). After the first
capture, the player moving next may not capture immediately, as this would repeat the
board position; instead, that player must play elsewhere on the board (or pass). The
player who first captured may then "fill" the ko (or otherwise resolve it), or play
elsewhere as well (often in response to the other player's previous move.) If the board
position has changed, and the ko has not yet been resolved, the opponent is then free
to capture, and it is the original player who may not then immediately recapture. This
process is known as a ko fight, and the moves played away from the ko itself are known
as ko threats.
Figure 3. Ko
Rarely, multiple kos or other repetitive situations will arise; the principle for handling
them is always the same: the players must avoid repeating the full-board position, so
they are periodically, and alternately, forced to play away from the repetitive situation
before responding.}

Which does not specifically say that a player is allowed to pass and thus re-produce a board position. However, reading further:

8) Illegal Moves: An illegal move is one violating the rules. If a player makes an
illegal move--such as moving twice in a row (i.e., before the opponent has made a
response), attempting to play on an occupied intersection, self-capture, or
retaking a ko so as to repeat the full board position, the player must take back his
or her move (both moves, if he or she moved twice in succession), it shall be
treated as a pass, and a pass stone exchanged.
An illegal move must be noted as such by the opponent before he or she makes
his or her move. When a player moves, he or she is tacitly accepting the
opponent's previous move as valid. In particular, if it is discovered that an earlier
move by one of the players was illegal, the game must nevertheless be continued
as it stands unless both players agree to restore the earlier board position and
proceed from that point.

So even if such a pass were an illegal move, Black could play it intentionally and then have his pass taken back and replaced by a pass How strange that player would be required to play an illegal move to win!

2) Play: The players alternate in moving, with Black playing first. In handicap
games, White moves first after Black has placed his or her handicap stones. A move consists in playing a stone of one's color on an empty intersection (including edges and corners), or in passing. Certain moves are illegal (Rules 5 and 6), but a pass is always legal (Rule 7).

Bill Spight wrote:It is not easy to write clear, consistent rules. Rule 6) could be more carefully stated. However, the writer or writers probably relied upon Rule 2) and did not worry about being punctilious.

2) Play: The players alternate in moving, with Black playing first. In handicap
games, White moves first after Black has placed his or her handicap stones. A move consists in playing a stone of one's color on an empty intersection (including edges and corners), or in passing. Certain moves are illegal (Rules 5 and 6), but a pass is always legal (Rule 7).

Emphasis mine.