4.2 The Last-Competitive-Move Rule (1)
Let us attempt to formulate area rules III. The single problem
confronting us is how to define the last competitive move. Under area
rules every move that occupies a neutral point is worth one point, so
our definition of the last competitive move will have to differ from the
traditional territory concept.
A reasonably understandable way to express the concept of the last
competitive move is to call it the last move that gains anything as
compared with letting the opponent play instead. This expression applies
both to traditional territory rules and to area rules, although perhaps
with some difference in meaning.
As a rule, however, this definition leaves certain doubts. The last move
that gains anything may be a comparatively clear idea to people who
understand the game of go, but it is inappropriate as a definition in
the rules. Let's look at some examples that show how unclear it can be.
Suppose that after White 4 in Dia. 4-1, Black plays 5 at 'a' for safety.
Which was the last move that gained anything: White 4 or Black 5? That
is not an easy question. This position is borrowed from a professional
game in which Black ignored White 4 in order to connect a ko. White than
played diagonally at 'b,' followed by moves in alphabetic order through
White 'k,' which was quite a disaster for Black.
If Black plays correctly he wins the capturing race, but in a game
between amateurs, it would take a lot of study of different variations
at the end to decide whether Black 'a' was necessary (in which case
Black 5 was the last competitive move) or not (in which case White 4 was
the last competitive move).
You may verify that Black is safe if he plays 'f' at 'h.' Accordingly
Black 'a' is unnecessary and White 4 is the last competitive move of the
As a second example we can take the game on a nine-by-nine board between
Go Seigen and Miyamoto Naoki presented earlier. This game, shown again
in Dias. 4-2-1 to 4-2-4, was played by traditional territory rules and
ended at White 80. Black removed the White group in the lower left by
actually capturing it and won by four points. You should check that
under area rules II Black wins by five points. If the game is played out
under area rules, it ends with Black 'a,' White 'b,' Black 'c' in Dia.