Newsgroups: rec.games.abstract
Date: Tue, 17 Nov 1992 01:56:28 -0500 
From: "Jonathan R. Ferro" <jf41+@andrew.cmu.edu>
Subject: TWIXT rules, and some strategy

Hopefully this post will be the final word on the basic rules and
terminology questions about this game, so that we can get on to the
meatier strategy considerations.

Here are the rules as Avalon Hill printed them in the Leisure Time Games
version:

----------

HOW TO PLAY TWIXT (for two players)

1. Red plays first.  Players move alternately by placing _one_ peg at a
   time on the board.  Pegs may be placed by a player in any empty peg
   hole except those inhis opponent's border row.

2. When, after he has placed a peg, a player finds that he can _link_
   two or more of his pegs, he may place one or more links between these
   pegs to make a barrier.  Pegs may be linked only when the distance
   between them corresponds to the diagonal of a 6-holed rectangle.

   [ Diagrams "Twix--the basic linking move", "Eight possible linking
     directions from a given peg", "Double-Link (numbers indicate order
     of placement)" not included.  The Double-Link diagram shows how the
     third peg can be bridged to both the first and second pegs. ]

   A barrier cannot be crossed.  No barrier exists where a player could
   have linked but did not--whether the omission was intentional or
   unintentional.

   Before placing a peg, a player may, if he desires, carefully remove
   any pegs and links he has previously placed on the board.  However,
   he should be certain not to remove any pegs and/or links which would
   give the opponent the advantage.

3. To win, a player must connect his borders with an uninterrupted chain
   of linked pegs.  If neither player can complete such a barrier, the
   game is a draw.

HOW TO PLAY DOUBLE TWIXT (for four players)

Double TwixT is TwixT for four players in teams of two.  Rules are the
same as for TwixT, with the following qualifications:

1. Partners sit opposite one another.  Play alternates counterclockwise
   around the board.

2. No partner is limited to any one sector of the TwixT board: partners
   may play the two ends of a common barrier, or they may build
   independent sectors on any part of the board.  Partners may not
   communicate strategies to one another by any form of signalling.

3. Once, and only once in each game, on partner of either team may call
   out, "Privilege!" after making his own move.  On claim of Privilege,
   the opponent who would ordinarily move next must yield his turn to
   the other member of the "Privileged" team, giving the Privileged team
   two successive plays.

   The player to move next will be the partner of the opponent who
   yielded his turn.  If the opponents have not been defeated by the
   Privilege move, they may take their own Privilege at that point or
   later in the game.

   Privilege is invoked primarily for defensive reasons.  If this option
   is carefully planned by well-matched teams, it can make Double TwixT
   a fast, challenging game.

----------

Me again.

Note 1.  These rules ALLOW the removal of some of your structure at the
beginning of your move.  The ramifications of this have already been
discussed in another thread on this newsgroup.

Note 2.  The rules make no mention of play in the corners, despite their
existence in the AH board.  A cutthroat variation is to allow play
in the opponent's border row, with a corner being a legal border
connection for either player.

Here is the basic strategy session from the AH rules:

----------

BASIC SETUPS

A setup is a planned pattern of pegging which permits the player to
double-link in either of two directions during the third move.

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . *2. . . . . . . . . . . . . . . . . . . . . .2x . . . . . . . .
. . . ./.\. . . . . . _-*2. . . . . _-*2. . . . . . _-*-_ . . . . . . .
. . . o3. o3. . . .3o-./. . . . .3o-. .\. . . . .3o-_ . _-o3. . . . . .
. . . .\./x . . . x/_-o3. . . . . x\. _-o3. . . . . .-*-. . . . . . . .
. . . x *1. . . .1*-. x . . . . . .1*-x . . . . . . . x1. . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

      Beam         Tilt            Coign            Mesh
    (3 holes,    (2 holes,       (diagonal        (1 hole,
    straight)    diagonal)       of 8-holed       straight)
                                 rectangle)

Pegs are numbered in order of placement.  In the third move (o) of any
setup, a player can both peg and double-link.

Generally, it is easier to concentrate on the placement of the second
peg, rather than the whole pattern.  If the second peg is placed the
correct distance from the first, the alternate locations for the third
peg will be obvious.

The most important part of the strategy of a setup is to avoid wasting a
move.  Do not place the third peg until your opponent moves to bar one
of your linking alternatives.  Instead, concentrate on building another
section of your barrier.

A setup can be foiled if the other player moves to block it immediately
after the first peg of the setup is placed.  Such foils are extensive;
some possibilities are indicated by x on the diagrams.  A well-placed
linking move is the simplest foil for a setup.

----------

The AH rules also include a sample game on a reduced board which I am
not going to reproduce, except to note that the reduced board is 12x12
instead of 24x24, and does NOT show the existence of corner holes.

Despite the game clearly not being as complex as GO, much of the
terminology of GO applies well to its strategy.  The section above
covers the introduction to "connecting" and "making shape".  Other terms
which have broad application across many abstract games, such as
"sente", also work here.

The Beam and the Tilt are the best setups for moving quickly across the
board, but can be attacked easily by the x moves shown, among others.
The Coign is much more solid, the only direct block being a connection
across the points marked x in that diagram.  The Mesh and the
unmentioned "Anti-Tilt" (consider the o moves in the Tilt diagram to be
1 and 2, followed by either of the * moves as the double-link) are to be
remembered as methods to connect pegs that were originally placed as
defensive or blocking moves.

Whereas the first three (which I call "long") are usually attacked by
building a barrier between pegs 1 and 2, the last two ("short") can be
attacked effectively by blocking their possible connections to the
double-link spots _without_ actually separating them with a barrier
(this is the intention of the x moves on the "mesh" diagram; a "beam"
connection between the x's would smother a possible connection on that
side).  In tight situations this attack could be used against the long
setups also.

The primary weakness of long setups is the inability to link them
end-to-end.  In the situations below the moves x will quickly lead to
tight fighting and should be given consideration regardless of the
relation of x to the rest of your pegs, due to the devastation they will
cause in the opponent's barrier.

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . * . . . * . . . * . . . . . . . . . . . . . . . * . . . * . . . . .
. . . x . . x . . x x . . . . . . . . . . . . . . . . x . . x . . * . .
. . . . . . . . . . . . . . . . . . . . . . . . x . . . . . . . . . . .
. . . . . . . . . . . . . * . . . . . * . . x . . * . . . . . . . . . .
. . * . . . . . . . . . x . . . . . . x . . * . . . . . . . . . . . . .
. . . . . . . . . . . . . . . x x x . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . * . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

  Beam Beam   Beam   Tilt  Tilt  Tilt  Coign Coign Coign Beam Coign

A possible proverb: "Play inside the angle of linked setups".

The one exception to this rule is the linear Coign-Coign link, which
does not appear to have a single devastating countermove.  I have not
completed this analysis, but it seems that a similar result can be shown
for short setups and for combinations, but is complicated by the
possibility of smothering attacks as well as cuts.

The GO proverb "Do not touch what you are attacking" also applies to
Twixt, although in a different sense that is difficult to define.  If
your opponent has a free end heading straight towards her border it is
already too late to try to set up just one barrier to block her.  You
should skip at least 3 holes away ahead of her to start setting up a
more extensive wall.  (This is the area that I am very fuzzy in and will
expect to see the most advances in, similar to the development of chess
openings or GO joseki.)  Conversely, an opponent who plays too closely
to your free end is giving you a gift by letting you either (a) choose
which way to go around it with a single-link move or (b) make move 2 of
a setup on the other side of her peg, forcing her to make the decision
of which double-link connection to block.

-- Jon Ferro               Einsprachigkeit ist heilbar
Organization: Carnegie Mellon, Pittsburgh, PA