Newsgroups: rec.games.go
Subject: save-go and more...
From: chisnall@cosc.canterbury.ac.nz (The Technicolour Throw-up)
Date: 8 Sep 92 00:04:10 +1200
Distribution: world
Organization: Computer Science,University of Canterbury,New Zealand

I've had a few requests to explain save-go.  The game was described in article
on this group last year by Wilfred someone.  I appear to have lost the headers
on the article so I don't know his last name or address.  Here's what I still
have (followed by various comments of mine):
-----------------------------------------------------------------------------
Subject: Go variants

A variant of Go for you to think about -

In addition to the normal moves of Go, add a new move "save-move". Each saved
move can be used any time in the future.  So the player who has saved N moves
will be able to make upto N+1 moves as a single move.  Groups will still be
life with two eyes.  The rule for ko will not change either (that you may not
go through a previously occuring position).  Though if you have extra moves
saved up, you can make one move somewhere else to alter the board first and
then take back the ko and fill it if you still have extra moves left. 
However, you can't take back the ko first and then play the second move since
this moves through a previous position.  Thus taking back a ko and
immediately filling it will not be allowed --- hence you need at least three
stones to take back a ko.  It seems to me that all rules in Go can be
'preserved' in some interesting way this game.

Here is an argument that this game will not degenerate into either normal Go
or one where both players keep saving moves and never play the moves out. 
The value of an extra move is certainly greater than (with one move saved,
you cannot be caught in a ladder, for example, or you can threaten to cut
through bamboo joints) going first.  So, if nothing else, black should be
willing to play save-move on his first move.  Degeneration in the other
direction is also not possible, because there will be a point when a player
can use all of his saved moves and make live groups everywhere.  So optimal
play occurs somewhere in between.

I played this acouple of times and found it very hard.  Anyone else had tried
this?

I wonder what's the computational complexity of this game?

Wilfred
-----------------------------------------------------------------------------

I hinted in my previous message that its possible to generalise this.  In
ordinary Go you can't save any moves at all while in save-Go you can save any
number of moves at all.  Define n-th order Go to be like save-go except that
there is an upper bound of n on the number of moves that any player may have
saved at any one point.  Ordinary Go is then just 0-th order while save-go is
infinitieth-order Go.  (Note that by the argument in the second paragraph of
Wilfred's article it follows that for a fixed size board there is some k such
that for all m >= k  m-th order Go is effectively the same game as save-go. 
I point this out because in complexity theory you're usually concerned with
programs that can play on any size board.)

I'm personally inclined to suspect that save-go may be too hard for humans to
play but 1st, 2nd or even 3rd order versions may be playable.

There are two game constructors that I think are probably well known - the
"misere" constructor and the "-spiel" constructor.  For many games X it is
possible to come up with misere X or X-spiel versions.  It seems to me that
the "n-th order" idea is another constructor (with the "save-" constructor as
a special case) - one can easily envisage nth-order and save- versions of
chess and checkers for example.

Any thoughts on the complexity of save-go or the nth-order versions?

--
Just my two rubber ningis worth.
Name: Michael Chisnall  (chisnall@cosc.canterbury.ac.nz)
I'm not a .signature virus and nor do I play one on tv.