You have understood the fundamentals of the game and can usually set up the correct number of chains. But are you are still losing consistently to Dabble and the better Yahoo players? Well, you have probably reached the big barrier separating good players and expert players, somewhere between 2000 and 2200 in Yahoo ratings.
The Dots strategy that I have described so far was simple: you try to set up the correct number of chains corresponding to your color. However, this strategy has limitations, and players may find that they are winning the chain fight, but losing the game.
There appear to be two important steps required to reach the expert level.
This step is the key to top level Dots play: Players must develop a catalogue of endgame positions and their values. In fact, this is also an important conceptual advance: Instead of just thinking ahead to achieve immediate goals, players must also learn to first visualize the endgame positions they want to obtain, and adapt their immediate move to reach that goal. That is, the strategical emphasis changes from simply making general moves delineating territory, into long range moves seeking to achieve specific endgames.
I will try to explain how to learn these two steps in this section. But, in order to assimilate it, you will need to work hard. First, you must learn all the endgame positions with quads. The only effective way to do this is to figure it out yourself by making a list of the endgames and going through them on your own. I will try to help you do this by outlining the basic results.
This may sound trite, but to get better, you will need to start playing with better players. You may have avoided doing this before, because it was depressing to lose all the time, but if your rating is getting around 2000, then you should be able to do better against Dabble and players rated about 2200, so playing them won't simply be a source for discouragement.
Playing Dabble is now more important than ever. Dabble will consistently be able to win with Yellow and tie with Green, despite having lost the chain parity fight. You must study Dabble's techniques and learn to prevent it from using them, as well as applying them in your games.
It is also time to start challenging players rated about 2200 or higher. You should be able to tie and even win a few games. However, players at the 2400 level can still probably beat you every game, so don't insist too much with them.
For example, in the above position, Yellow has managed to make
three chain, and appears to have the game locked up, since one
of the chains is already quite long. However,
Green can save the farm by moving in the unfinished chain
(he will have to be the first to move into a chain, sooner or later).
This effectively reduces the length of that chain, and leads to
a tie.
The preemptive sacrifice can easily be overlooked, and its unexpected
use can be a cause of some anxiety. These rules give some peace of
mind, since they say that you can't lose to it if
you aren't already 3 boxes down.
These rules also seem to indicate that a preemptive sacrifice is
most effective if it is played immediately after
your opponent has sacrificed some boxes in order to
win the chain fight.
In 6x6 Dots and other games with an odd total number of boxes,
it is possible to win using the preemptive sacrifice if you are only two
boxes ahead. For example, in this position, from the book
Winning Ways, Yellow is two
boxes ahead, so can use the preemptive sacrifice to win the game.
DIAGRAM
It is easy to check these rules by noting that accepting or declining
the preemptive sacrifice simply inverses the role of the players.
I give a
formal proof below for people who are interested in
seeing it.
When your opponent makes a preemptive sacrfice, you are faced with
the choice of accepting all the boxes, or leaving the last two
boxes making a doublecross.
In the first case, you simply continue with the basic strategy,
making the number of chains corresponding to your color.
In the second case, the early doublecross means that you have
made one chain and used it like you would in the
final phase. With one chain
done with, you need to make one less than you would normally.
In other words, for 5x5 Dots:
An early doublecross means a change of sides: Yellow must now get
make zero or two chains, Green must make one or three chain. This count does
not include the sacrificed chain.
Using basic algebra, let N be the total number of boxes (16 in 5x5
Dots and 25 in 6x6 Dots), Y and G be the number of Yellow and Green
boxes before the sacrifice, C the number of boxes in the sacrificed
chain. Let X be the maximum number of boxes that can be captured by
the side taking the last box in the chain. Since
X is the maximum number of
boxes the first player can attain in a Dots-and-Boxes game played on
the same board, but with the Y Yellow Boxes, G Green Boxes, and C
chain boxes removed, its value is independent of what Yellow and
Green did beforehand.
Without loss of generality, assume that
Green makes the preemptive sacrifice to win the game.
One has two possibilities:
In order for Green to win in both cases, the first Yellow
value must be less than N/2 and the second Green value
must be greater than N/2, that is
Subtracting Y + X + 2 from both these inequalities gives
Now, C must be at least 3, since chains have at least three boxes,
so one gets
Now, if N is even like in 5x5 Dots,
then the term in the middle is a whole number
so that the right and left sides must be at least two apart, that is
But if N is odd, like in 6x6 Dots,
then the middle term is half an integer and one
can only conclude
This proves the conditions for a win using the preemptive sacrifice.
The proof for ties is exactly similar.
To nibble means "to eat in small bites" and this technique can be
used effectively against an opponent who wants to get the
correct chain count at all costs.
For example, in this position Yellow seems to have attained all his
goals: With only two boxes sacrifice, he has formed a very long chain
and has prevented Green from making a second chain.
However, the game is a tie: Yellow will have to sacrifice two more
boxes to prevent a second chain, then will have to give up four more
boxes in the
short chain phase.
This example pretty well sums up the nibbling strategy:
Experienced players will note that the first method almost
always wins for Yellow when Green tries to prevent one chain
at all costs (instead of trying to make a second chain or cycle).
This is why Yellow usually wins when there is very little
space to make chains, for example, after sacrifices filling up
the center.
The second method appeals to the Short Chain
Rule which guarantees the short chain advantage to the player
losing the (long) chain fight. You must use this advantage to save
the Dots war, once you've lost the chain battle.
The theory is simple:
If you take the quad (from a one edge offer) then you give up control.
To keep control, you must decline the quad. This means:
Well, that is the theory, now for the practice. Understanding
the quad is not too hard, because the first person to move into
a chain or quad will usually move into the quad first. It then comes
down to analyzing what happens after the quad is taken. Note
that you only have to the count from that point on, since one side
or the other will have to take the quad, the rest of the moves
will be the same no matter who took the quad.
It seems to me that the quad is has a levelling effect in most
situations. The reason is that the player taking the quad will earn 4 points,
and the player giving up the quad will usually take the last chain,
so usually 4 points, so there is a fairly balanced split.
This levelling effect implies that
sacrifices must be used very sparingly
when there is a quad around. In particular, the
preemptive sacrifice cannot be used
when there is a quad, because acceptance gives at least 3 points,
yielding 7 points when added to the guaranteed 4 points in
the final phase. This almost certainly means a win for the person
accepting the preemptive sacrifice.
The basic situation with one quad
can be completely characterized completely for 5x5
Dots (4x4 boxes). One has the following rules, which assume that all
the capturing of short chains, chains, and quads is done at the very
end (no sacrifices). I will also assume that chains do not terminate
in quads (this usually gives the advantage to the winner of the chain
fight):
Two quads is also fairly easy to understand and
the situation can be characterized completely for 5x5
Dots (4x4 boxes). One has the following rules, which assume that all
the capturing of short chains, chains, and quads is done at the very
end (no sacrifices). I will also assume that chains do not terminate
in quads (this usually gives the advantage to the winner of the chain
fight):
Knowledge of these rules should make it a lot easier to solve the
above Dots problem. In Problem Q1,
Yellow wins somewhat unexpectedly by immediately
making a chain of length 4, which disconnects this chain from the
bottom row. No matter where Green moves next, Yellow will be able to
separate the bottom row into two disconnected parts, each of which is
a short chain, and so a win for Yellow, by the third rule.
Any other Yellow move will allow Green to keep the number of
short chains down to one.
In particular, Yellow can move into the position of Problem Q2.
Green now ties by moving
into the bottom edge, second on the left. This threatens
to make a join with the chain. If Yellow stops this by disconnecting
the chain, then Green makes a second chain and wins.
Kermit's lament has never touched so many hearts as in 5x5 Dots
game rooms. Indeed, the second player has a very difficult time
holding his own. Computer analysis
shows that Green only has two correct responses to Yellow's
strongest first move, whereas Yellow has absolutely no theoretically
losing move until his third turn.
A perhaps more compelling reason for Green's sorrow is that he
will usually make two chains, sacrificing two boxes in one of them,
therefore giving Yellow a two box handicap. For example, Yellow is
more than ready to sacrifice two boxes to ensure one chain, usually
winning the game if he can achieve his chain goal. On the other hand,
if Green sacrifices two boxes to ensure two chains, then he will be
already be at a four box disadvantage, due to the doublecross he will
give away at the end, so he will have difficulty winning if his chains
are not very long.
Another Green disadvantage is that the preemptive sacrifice
will always fail against a unique chain, since accepting all
the boxes leaves zero chains, which always favors Yellow,
by the zero rule.
However, the strategies outlined in this section, the
preemptive sacrifice,
nibbling, and the
quad are exactly the
ticket to help Green.
It seems that the best way for Green to save the day is to
know a number of "saving positions" and try to reach these.
The methods of this section give a few such positions which
I call "standard ties".
The standard ties have very similar counterparts which are
losses for Green, and he must be aware of these to defend
correctly. Yellow, on the other hand, will try to reach
these positions.
Aftermath
Skip This Proof
In this section, I prove the fact that you must be at least
three boxes ahead to win using the preemptive sacrifice on
a 5x5 board, and two boxes ahead on a 6x6 board. You should
look this over only if you have an abnormal mathematical curiosity.
Nibbling
The Quad
One Quad
Two Quads
It's not Easy Being Green
Standard Ties
Standard Losses
Next Section