[pbmserv] New (non-server) game: XANA

[Bill Taylor <W.Taylor@math.canterbury.ac.nz>]

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                          New Game - XANA
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This flyer is to introduce a new game, invented by Joao Neto (jpn),
with modifications by Bill Taylor (kiwibill).   We think it is excellent.

It started out as a variety of Go, but though it still has something
in common with its parent, the whole "look and feel" of the game is
quite different and deserves to be known as a separate game idea.

On a hexagonal board, players move in turn doing each of the following,
in order, either of which can be passed.  Firstly, drop a stack of counters
(or stones) onto a cell occupied by one's own stones, or onto an empty cell
in a region of one's own territory or unclaimed territory.  Secondly,
drop two neutral stones (walls) onto empty cells not too far from
a stack of one's own; these walls can never be removed or moved again.
The counter-dropping part of the move can be replaced by a movement of
a stack or part of a stack of friendly counters, to a friendly stack
or empty cell that is not too far away.

Any connected region of empty cells that can be reached from ONLY one's
own stones, by some track of empty adjacent cells, counts (temporarily)
as one's territory; and is forbidden to the opponent for drops or moves
of counters or walls.    But these territories may become neutral again
if one of the border cells is a stack of counters that later moves away!

There is an endless supply of walls, but a strictly limited supply
of one's own counters, so it is unwise to be TOO profligate with them!
The size of the supply is determined by the size of the board;
we have generally found it nice to play on the 8-cells-per-side
board illustrated below, with 169 cells.

Captures can also be made, if a stack of opponent stones becomes
surrounded by non-empty cells of any type.  Captured stones, and
empty cells in one's own final territory make up one's final score,
as in Go with "Japanese" style scoring.

These various features - stone movement, neutral walls, limited stone
supply, and forbidden regions - make the game so markedly different
from Go, that it is best to regard it as an altogether different game.
It is purely about region-building, and very strategic, with none of
the intricacies of the cut-and-thrust and eye-formation of Go.

We strongly urge all abstract gamers to try it, either on home-made
boards or by email, and hopefully it will eventually become a standard
on the pbem server.  The "X" is pronounced like a hard "h" sound, though
we will not object if you say "ksana" quietly to yourselves!   ;-)

The game is attractively displayed at Joao's website
                         http://www.di.fc.ul.pt/~jpn/gv/xana.htm

Here is the formal set of rules, and an example game.

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XANA is played on a hexagonal board of side-length N.
Each player has 2N stones. There is an endless supply of walls.

* Accessibility: Any empty cell X is accessible to a player on his 1st move;
  or if it is stepwise connected by empty cells to some friendly stack.

* Circle: The circle of stack S (with height H) is all cells accessible to S
   at Hex-Euclidean distance (from S) of less than or equal to H.

At each turn, each player may do two actions:

1) (Optionally) insert or move a friendly stack.
  * A stack (1+ stones from off board) is inserted at an accessible cell.
  * Any stack must be adjacent to an empty cell,
                                   unless it produces immediate captures.
  * A stack may move to an empty or friendly cell of its own circle.
  * A stack may move only part of its stones (thus splitting in two).
  * A drop may be onto a friendly stack.
  * If a stack splits, the distance travelled by the moving part is
    up to the circle radius of the moving part only.

2) (Optionally) insert up to two walls on friendly circles.
   Any stack not adjacent to an empty cell, is immediately captured.

There is a swap option on the first move.
When both players pass, the player with more points wins. Score 1 per cell
accessible to the scoring player only, and 1 point per captured enemy stone.

...................................................................

In the following game, the cells are co-ordinated orthogonally;
   . . 1 . # . . . . # # . j12 11  lj11  + k10 x7:1 h9q12  + v9  y8
    . . # # # . . . . . #      12  v8v10 + x11 y12  q12l13 + u10 v11
     . . # 1 A . . . . .       13   An13 + k12 j13 5l13h11 + l11 i12:3
      . . . # . . . . .        14   Al15 + m12 m14  4h7f11 + i6  i10
       . . A . . . . .  j28    15
                                    prisoners captured by...  Joao 2
abcdefghijklmnopqrstuvwxyzABC                                 Bill 7

Remaining in store:   digit  stones:  3
                      letter stones:  1

COMMENT: The game was fairly even until Bill made a major mistake on move
13, leaving Joao with the huge territory capture of 28 in the lower right.
Bill resigned soon after.

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