1996-10-9 last update, 1996-10-9 first day
Robert Jasiek,
jasiek@berlin.snafu.de
Copyright: All rights of the author are preserved according to the
international law.
Examples 5
Introduction
This page gives examples with comments referring to the
Prohibition Rules. Note that the
prohibition rule of the Prohibition Rules is slightly
different from any prohibition rule in any other set of ko rules.
Conventions are defined.
If all kos on the board are basic kos, then the prohibition
rules allow the same moves as the Basic Ko
Rules. Such examples can be found on
Examples 4. With one or more ko strings of
more than one stone on the board analysis is different. Such
examples are presented on this page.
If a whole string should have marks on it, just ignore them;
they are immaterial.
Examples
Several kos; at b-c-d-e shall be a B string,
at g-h-i-j shall be a W string
- 6 kos are on the board.
- The kos are a-b-c-d-e, f-g-h-i-j, k-l, m-n, o, and p.
They consist of 5, 5, 4, 4, 4, respectively 2 board points.
- 7 ko strings are on the board.
- The ko strings are b-c-d-e, g-h-i-j, k-l, m-n, M, the two W
stones of o, and p.
- M is not a complete ko string. All other ko strings are
complete. B[o], W[a], or B[f] would give other complete ko
strings.
- p is the only basic ko shape. All other shapes are scarce.
- Some of the ko strings are just ko strings for the purpose
of the rules, but will not be treated as ko strings in a
reasonably played game.
- Now possible MSs will be analysed that may occur between
board plays that are no ko stones. Any tenuki from all kos
will change the configuration of the stones on the union of
all board points that are not part of a ko. Then prior
restrictions due to the prohibition rule no longer apply for
the time being. Instead new restrictions will have to be
considered. A connection of a ko string to a string of the
same colour would have the same meaning for the rule as a
tenuki from all kos.
- B[fabgc]# is prohibited by rule of prohibition, because it
is the second ko stone of B played in the ko a-b-c-d-e
during the MS.
- W[kml]# is prohibited, because it is the second ko stone of
W played in the ko k-l during the MS.
- B[okmon]# is prohibited, because it is the second ko stone
of B played in the ko m-n during the MS.
- W[pmkpafp]# is prohibited, because it is the second ko stone
of W played in the ko p during the MS.
- It is reasonable to consider a and f as miai and k and m as
miai and to expect W[op] before the end of the game.
- As the above MSs show the prohibition rule prohibits
superfluous moves.
- It may require some reading to detect if a string is a ko
string. But it is easy to see by intuition that it is not
worth playing in a-b-c-d-e, f-g-h-i-j, k-l, or m-n. Until
a player decides to play in one of these kos, it is not
necessary to apply the definition of cyclical MS precisely.
A ko-string-free repetition
- No ko string is on the board.
- A B stone at a will be no ko string, since it will have no
cyclical MS. Any non-empty MS leading to a repetition is
required to contain a pass play.
- B[apb]# repeats the whole board position (which is the same
as the configuration of the stones on the union of all
board points that are not part of a ko).
- The text of the prohibition rule referring to a play of a
stone that is no ko stone prohibits B[apbpa]#.
- B[apbpb]# is allowed, but B[apbpbpapa]# or B[apbpbpapb]# are
prohibited.
- Superfluous suicides cannot create an infinite game.
- If both players should have the possibility of superfluous
suicides in another example, then in theory MSs that are not
of only linear lengths would become possible. However, only
the losing player has an interest of a prolonged game. The
other player will virtually restrict himself to pass plays
so that repetition will only occur after MSs of linear
lengths.
- Til today the only known example with similar features, but
more reasonable and pass-free play is molasses ko. In
molasses ko not only ko stones are played, but the position
repeats.
At b shall be a B stone, at d shall be a W stone
- The so called eternal life is a ko of 4 board points.
- B[acb]# is prohibited, because it is the second ko stone of
B played in the ko during the MS.
- A proper ko fight is B[acttbdtt..].
A strange triple ko
- Three kos a-b, c-d, and e are on the board and consist of
4, 4, respectively 2 board points.
- B[acb]# is prohibited, because it is the second ko stone
of B played in the ko a-b during the MS.
- B[ecad]# is prohibited, because it is the second ko stone
of W played in the ko c-d during the MS.
- B[ecaeb]# is prohibited, because it is the second ko stone
of B played in the ko a-b during the MS.
- B[aced]# is prohibited, because it is the second ko stone
of W played in the ko c-d during the MS.
- Thus in this strange example it is best not to try keeping
things very simple by [ettett..], but to eliminate local
ko threats in a-b and c-d first and then to capture in e:
B[acettdbacettdbacettdbacett..].
[to be continued]
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