RE: computer-go: Live or Die

[Jean-Pierre Vesinet <jvt@xxxxxxxxxx>]

	Thank you for your answers.

	It seems we have some misunderstanding about regions and their
safety.

>  I think you must allow them to overlap. Otherwise you get into trouble.
> What is a region, and what is not? E.g. make a black wall horizontally
> across the whole board, and a white wall vertically, with a cross-cut in
> the center. What would be your regions? I have two black regions and two
> white ones, which overlap each other on a quarter of the board.
> 
> A more realistic example is a dead white group with one eye. It is a white
> 1-point region
> within the black region that contains the dead group. If you want to
> eliminate these you must know a lot about Life and Death....
> 
	Sure. What I meant by "not allowed to overlap" was defined in :
> >- A c colored region is a maximum connected set of -c and empty points.
	This prevents a White region overlapping another White region, and
the same for Black.

	For example there are only two Black regions in this diagram, not
three:

	|XXXX   (bottom-left corner)
	|   X
	|XX X
	| X X
	+----

> The other question, "regions in which neither player ever needs to play",
> is much much much much harder. It involves knowing everything about life
> and death, seki, ishinoshita, double ko, semeai etc.
> 
	Well, I'm still struggling with the basics, such as the "Safety of
areas surrounded by safe blocks" on page 63 in your PhD thesis. These
regions and Benson-safe regions share the interesting property that no move
in them is _ever_ useful (both players can safely ignore them). The defender
can tenuki, because no defensive move is necessary, and the attacker would
just loose a move. In all the other cases attacker's or defender's moves may
be useful. For example an attacker's move in a settled region may be useful
as a ko threat, seki doesn't stay seki if an atari is not answered, etc. Am
I right in assuming there is no other class of region with this property ?

	[Jean-Pierre Vesinet]