1996-10-5 last update, 1996-10-5 first day
Robert Jasiek,
jasiek@berlin.snafu.de
Copyright: All rights of the author are preserved according to the
international law.
Examples 4
Introduction
This page gives examples with comments referring to the
Basic Ko Rules.
Conventions are defined.
If a whole string should have marks on it, just ignore them;
they are immaterial.
Examples
Basic ko
- a together with the point right of it is a ko. This is the
only possible ko shape by definition.
- W[aa]# is prohibited due to the basic ko rule.
- W[attatt..] is allowed.
Double ko
- Two kos a and b are on the board.
- B[aa]#, W[bb]# or B[abb]# are prohibited due to the
basic ko rule.
- Conceivable board plays are limited to the union of the two
kos a and b. The rest of the board remains unchanged. This
is important for the prohibition rule. Also the set of board
points of the union of all kos does not change.
- After B[abpabp] B has captured stones in a and b and W has
captured stones in a and b. Due to the prohibition rule
B[abpabpa]# is prohibited. The game ends after B[abpabpp].
The game might have better ended after B[pp] only.
Triple ko
- Three kos a, b, c are on the board. A tenuki, that would
change the rest of the board, is not possible. The only
board plays reasonably available are ko captures.
Each player can capture once in each ko. Then the
prohibition rule does not allow a further ko capture.
Altogether 6 ko captures are possible.
- The prohibition rule restricts play to W[acbacbpcpp].
- W[pcpp] gives the same result.
Three kos
- a, b, c are the three kos on the board. The union of all
board points of all kos on the board consists of the 6
board points of the 3 kos. All other board points form
the rest of the board.
- The players may decide to treat a and b as miai and to
fight for c only: B[cttctt..]
- If both players stubbornly insist on capturing stones in
kos, they will be trapped in prohibition after 6 moves:
B[cbacba] and no ko capture by either player remains
untouched. The next move must be a play elsewhere:
B[cbacbat]#. This changes the rest of the board. So now
stubbornness might reappear: [..cbacba]. But only for 6
moves.
Triple ko
- B cannot capture W: After B[acbacb] the prohibition rule
applies. It is a coexistence.
- Even if a is external, but still adjacent to the big W string,
it is a coexistence.
Moonshine life
- B cannot capture W with B[abcabc] due to the prohibition
rule.
Sending-2-returning-1 and bent-4
- No ko is on the board. However, repetition might occur and
will be restricted by the prohibition rule. The phrase
"nor play another move on a distinct board point" applies
for repeated board positions (except board points in kos,
but here are none).
- B[acapa]#, B[bcbpb]#, B[acapbcbpa]#, and B[acapbcbpb]# are
forbidden by the prohibition rule.
- If the last stone played was the B stone on a, then also
W[paca]# would be prohibited.
Quadruple ko
- W[acbdcbdapp] leaves the position in coexistence as well as
W[pp].
Ring of 4 basic kos
- This is a coexistence. Before the game end not more than 8
ko captures will be possible.
Molasses ko
- a is the only ko on the board. During cyclical play only
a and b can become kos.
- B[cadbpcbdapdacb]# is the first prohibited move in the MS.
W loses.
- B stones at c respectively d give different rests of the
board. Therefore, even tough after [..pd]# the union of all
kos is only the ko a, [..pda]# is also allowed.
Exercises
Four kos
- What will remain on the board?
At b shall be a B stone, at d shall be a W stone
[to be continued]
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