(;GM[1]FF[3]
RU[Japanese]SZ[19]HA[0]KM[4.5]
PW[White]
PB[Black]
GN[White (W) vs. Black (B)]
DT[2000-07-03]
SY[Cgoban 1.9.5]TM[30:00(5x1:00)];
AW[ca][ga][ka][oa][cb][gb][kb][ob][ac][bc][cc][gc][kc][oc][sc][ad][bd][cd][dd][ed][fd][gd][kd][od][pd][qd][rd][sd][ae][ee][fe][ge][he][ie][je][ke][le][me][ne][oe][pe][ff][if][pf][fg][ig][pg][fh][ih][ph][qh][ai][ei][fi][ii][ji][ki][li][mi][ni][oi][pi][qi][ri][si][aj][bj][cj][dj][ej][fj][gj][hj][lj][mj][nj][oj][pj][qj][dk][gk][lk][mk][qk][dl][gl][ll][ql][dm][gm][lm][qm][dn][gn][hn][ln][qn][co][do][go][ho][io][jo][ko][lo][mo][qo][ap][bp][cp][dp][ep][gp][hp][ip][jp][kp][lp][mp][np][op][pp][qp][rp][sp][aq][eq][fq][gq][kq][pq][er][kr][pr][es][ks][ps]
AB[ba][da][fa][ha][ja][la][na][pa][sa][ab][bb][db][fb][hb][jb][lb][nb][pb][rb][sb][dc][ec][fc][hc][jc][lc][nc][pc][qc][rc][hd][id][jd][ld][md][nd][be][ce][de][qe][re][se][af][bf][df][ef][jf][kf][lf][mf][nf][of][qf][ag][eg][jg][og][qg][rg][ah][bh][dh][eh][jh][kh][lh][mh][nh][oh][rh][sh][bi][ci][di][ij][jj][kj][rj][sj][ak][bk][ck][hk][ik][kk][nk][ok][pk][rk][cl][hl][kl][ml][nl][pl][rl][cm][hm][im][km][mm][pm][rm][bn][cn][in][jn][kn][mn][nn][pn][rn][ao][bo][no][oo][po][ro][so][bq][cq][dq][hq][iq][jq][lq][mq][nq][oq][qq][rq][sq][ar][br][dr][fr][gr][hr][jr][lr][or][qr][ds][fs][js][ls][os][qs]
C[Why did I loose THAT group?!?!
     (An Eye Shape Tutorial)
             by Gus Heck

In order to get the most from this tutorial, you should
be familiar with the rules of Go, and understand when
stones are captured and should be removed from the
board. If you understand why groups with two separate
eyes (surrounded points) cannot be captured, you are 
ready. 

Let's Begin! 
]
;B[tt]
C[THE SITUATION: White has one large, live (uncapturable) group. 
Black has 16 groups, all of which are surrounded by live white
stones. Black cannot escape and cannot form a connection 
between any two groups.

OUR MISSION: Categorize these 16 groups in a way that helps
us decide where black should move. The categories are:

1. IGNORE - Groups that cannot be saved and should be abandoned
2. NOW - Groups that can be saved, if attended to immediately
3. LATER - Groups that can be saved and do not need immediate attention.

]
;W[tt]
C[First look at the upper left group. It has an eye at A1. 
Black cannot add any stones to this group, and thus
black cannot make it any safer. Without capturing 
the opponent's stones you NEVER can make an eye
bigger. Eyes only get smaller.  This eye is as small as
an eye can be and thus there is nothing we can do
to improve it. This eye  automatically falls into 
the first category.

IGNORE surrounded groups that have a one point eye.
]
;B[tt]
C[Obviously, groups with only one eye that
are surrounded are dead. Infact they can be captured
immediately.
]
;W[aa]
C[Now look at the group around E19. Black has done
a little better here, surrounding 2 points. However
There is nothing black can do to help this group...
]
;B[eb]
C[As soon as Black tries to add a stone to this group,
it becomes a one point group, and we know what
happens there...
]
;W[ea]
C[White captures - IGNORE all surrounded groups with
2 point eyes.

Now look at the group around J19. This group has 
three points. The shape is that of a straight line.
The straight three is the first group we have looked
at that can be saved. Black can easily divide it into
two eyes.
]
;B[ib]
C[Finnally a group that CAN be saved!. White would commit
self capture attempting to play at J19 or at J17. So this group
shouldn't be ignored, but does it need attention now or later?

To answer this question, lets look at the group around N19.
It is identical to the original form of the J19 group. But this
time we have ignored it (in favor of saving the J19 group).
Now white goes first...
]
;W[mb]
C[White knows exactly where to play. If white had played at N19 
or N17 black could have captured and formed two eyes in the
by playing n18. On this space however white cannot be
captured immediately.
]
;B[tt]
C[If black plays at N19 white will play at N17 capturing
all the black stones. If black plays N17 white will play
N19 also capturing, so black must wait for white's
next move.
]
;W[ma]C[Now black can capture, but...
];B[mc]
C[the capture is in vain.
The resulting eye shape is a 2 point eye. 

Do not ignore this shape

NOW is the time to save surrounded groups with the 
three-points-in-a-line eye shape.

You won't get to save it later.
]
;W[mb];B[ma];W[mb]
C[Lets examine the other possible 3 point eye shape:
The three-points-in-an-L shape. the group in the
upper right (around S19) is an example of this shape. 
So is the group directly below it (around S14).

Like the three-points-in-a-line the three-points-
in-an-L can easily be given 2 eyes if it is black's turn.
]
;B[qa]C[But if it is white's turn....
];W[sf]C[Now black will die.
];
B[tt]
C[Again any move by black leads to immediate capture.
Black must wait....
]
;W[rf]C[Black can capture.
];B[sg]
C[But once again, the Three point shape has been reduced
to a 2 point shape. 

NOW is the time to save the three-points-in-an-L.
]
;W[sf]
C[White's (attacking) strategy in all of the examples you will see
is to give away stones in a way that reduces a large eye shape
to a smaller eye shape.
]
;B[rf]
C[You may also have noticed that the saving move for black,
is on the same point as the first move white uses to begin 
the killing sequence. This is not a coincidence. The point
that saves or kills a shape is called the critical point. 
]
;W[sf]
C[An eye shape has a critical point when  there is only
one move that can divide the eye shape into two parts.

]
;B[tt]
C[If there is more than one place to divide the eye shape
Then white can't kill it.

To demonstrate this lets look at the four-in-a-line shape
that surrounds M13. 
]
;W[ng]C[If white plays in the end of a four in a line...
];B[mg]
C[Black can capture and form 2 eyes in the same move.
];W[sl]
C[If white plays in the center of a four-in-a-line, then
black cannot capture him immediately...
]
;B[sm]C[But black can still form 2 eyes.
];W[tt]
C[So are all shapes with four or more points safe?
Nope! The four-in-a-square shape (around 
T1 or O1) can'te even be rescued if black plays first!
]
;B[sr]
C[Anywhere black plays reduces the four-in-a-square to
a three-in-an-L shape, and now it is white's turn.
]
;W[rs];B[tt];W[rr];B[ss];W[rr];B[rs];W[rr]C[So black can't save it.
];
B[tt]
C[If black refuses to form the three-in-an-L shape.
White can force him into it.
]
;W[ns];B[tt];W[ms];B[tt];W[mr]
C[Now black is about to be captured and must do something!
];B[nr]
C[But now it's white's turn again.
];W[ms];B[tt];W[mr];B[ns];W[mr];
B[ms];W[mr]
C[The four-in-a-square shape is dead. It cannot be saved.
Therefore attempting to save it is wasting stones.

IGNORE surrounded groups that have a four-in-a-
square eye shape. They are dead. Let them rest in
peace.
]
;B[tt]
C[So now lets examine another four point shape.

The groups surrounding A1 and J1 Are the 
four-in-an-L shape. 

White can't hope to kill a group if he gets captured
as soon as he enters. Getting a single stone captured
usually gives the oponent a second eye. Therefore white
doesn't want to play at G1 or J2. Lets try J1.
]
;W[is];B[hs]
C[That didn't work at all. lets try again. on the other 4-in-an-L.
C1 would be the same as J1, so lets try B1.
]
;W[bs];B[cs]
C[Foiled again. - There is no critical point.

Even when surrounded, the four-in-an-L is perfectly safe.
We can deal with it LATER _if_ white attacks.

There is actually one situation in which this shape can be killed.
That occurs if it is turned the wrong way and jammed into the
corner. How this special case lives or dies involves the more
advanced topic of Ko fighting, so it is beyond the scope of
this tutorial.
]
;W[tt]
C[There is only one more eye shape with four points that 
has a critical point.  That is the four-in-a-T shape, 
seen around P7 and K8.

If black moves at J8 he converts to a three-in-a-line on white's turn.
If black moves at K7 or K9 he converts to three-in-an-L  on white's turn.

Both of those shapes are dead if white moves first.

The only other possible place for black to play is K8.
]
;B[jl]
C[This move actually creates three eyes. Overkill (overlife?), but
one can only have too few eyes, never too many.

Of course since there is only one saving move for black,
the same move is  killer for white.
]
;W[om]C[Any move by black now reduces to a dead shape.
];B[ol];W[nm];
B[on];W[nm];B[om];W[nm]
C[So the moral is:

NOW is the time to save the four-in-a-T shape.
];
B[tt]
C[There is also an S shaped 4 point eye shape but it
has 2 places it can divide into 2 eyes and is perfectly
safe. I don't have room to show it here.

Now we enter into the realm of Five point shapes. 
There are 9 possible five point shapes. Only 2 of
them have a critical point. 

The first one is the four-square-plus-one shape.
This is shown here around A7.
]
;W[am]
C[This is the critical point. If black had played here he would
have split the 5 point eye into a three point eye (A8,B8,B7)
and a one point eye. (A6). Now that white has taken that away
black doesn't want to convert to a four-in-a-square by playing
A6. Black also doesn't want to convert to a four-in-a-T by
playing B8.
]
;B[al]
C[Black will try to convert to the saftey of a
Four-in-an-S shape. The S shape is safe if
it is empty, now that white has both a stone
in the center of the S, and it is his turn
it is no-longer safe.
]
;W[bm]C[Now black must wait. To move would allow capture.
];B[tt];
W[bl];B[an];W[bm]
C[Notice how white has reduced the 5 point shape
to a more easily killed 3 point shape.
Black is stuck again.
]
;B[tt];W[bl];B[am]C[And now to a 2 point shape.
];W[bm];B[bl]
C[And now a 1 point shape.
];W[bm]
C[And finnally captures. The weakness of the four-square-plus-one
shape is exactly what it's name implies. It is almost a four square.
]
;B[tt]
C[Now for the other killable five point shape.

This one could be called the five-in-a-cross.
Other names include the star-five and the radial five.

]
;W[cg]C[This is the critical point. Lets watch it get killed.
];B[tt];
W[cf];B[tt];W[ch];B[tt];W[bg];B[dg]C[four-in-a-T
];W[cg];B[tt];W[cf];
B[tt];W[bg];B[ch]C[Three-in-an-L
];W[cg];B[tt];W[cf];B[bg]C[Two
];
W[cg];B[cf]C[One
];W[tt];B[tt];W[cg]
C[lift off 
(lift the stones off the board)

];B[tt]
C[Now lets look at the only six point eye shape that can be killed. 
]
;AE[cg]AB[be][ce][de][af][bf][df][ef][ag][eg][ah][dh][eh][bi][ci][di];
W[cg]
C[This is the four-plus-one-plus-one shape.
Many people call it the rabbity six because 
C14 and D13 look a bit like ears. At least to
some people it does. 

White has already attacked the critical point.
The killing of this shape is a bit trickier.
]
;B[bg]
C[With this move black threatens to make an eye around
B12. white must prevent this, by moving where black
wants to move. One can think of this as a second critical
point.
]
;W[ch]
C[Now anything black does will create a dead shape
we have already discussed. Now he must wait.
]
;B[tt]
C[Now white must be very careful. If white places a stone
at B12, black will live.

Here are the 2 possibilities involving B12:

white B12, black-pass/play elsewhere; 
THEN:
   if white D13, Black captures at C14 forming an empty four-in-an-S (live shape)
   if white C14, Black captures at D13 forming an empty four-in-an-L (live shape)

]
;W[cf]
C[This is a safe move for white.
D13 would have been fine too.
B12 is poison.
]
;B[tt]
C[Black must pass or move elsewhere or he 
will allow white to capture next turn.

B12 is STILL poison for white.
]
;W[dg]C[Now black must capture.
];B[bh]C[Four-in-a-T
];W[cg];B[tt];
W[cf];B[tt];W[ch];B[dg]C[Three-in-a-line
];W[cg];B[tt];W[cf];B[ch]
C[Two
];W[cg];B[cf]C[One
];W[cg]
C[So those are all the shapes that can be killed.
Everything else can be made live IF black's
stones are all connected, and IF the shape 
isn't jammed into the corner where white
can start a ko fight. And of course IF black
makes the right moves :).

Dead shapes shown here may survive if
they connect to another group with an eye,
Capture a neighboring stone(s) for a second 
eye, or simply build an eye on the outside. 

I hope this has been helpful. Good luck.
]
)
