(;FF[4]
CA[UTF-8]
GM[1]
GN[real versus false eye]
PC[https://online-go.com/review/72756]
PB[Black]
PW[White]
BR[8d]
WR[8d]
OT[Error: time control missing]
RE[?]
SZ[19]
KM[6.5]
RU[Japanese]

(;AB[ij]C[Middle of the board, one point eye

"ALL of the sides" means four sides.  Majority of the diagonals means at least 3 diagonals.

The key to an eye being “false” is that one or more of the surrounding sides can be peeled away if the opponent has enough moves.


-- chat --
Seryogo: 1. From move 0: J10 
cflinter: 6. From move 0: J10 
]
;AB[dd]
;AB[de]
;AB[df]
;AB[ef]
;AB[ff]
;AB[fe]
;AB[fd]
;AB[ed]TR[ed]TR[de]TR[fe]TR[ef]C[If E16 is a box, then the sides are the triangle points.

This eye at e15 has 4 sides and 4 diagonals.  It is a true eye.

Now I'll make some boxes with just sides ....

-- chat --
john.wpn: 3. From move 0: J10 D16 D15 D14 E14 F14 F15 F16 E16 
]
;AB[ie]
;AB[jf]
;AB[ke]
;AB[jd]
;AB[oe]
;AB[pd]
;AB[qe]
;AB[pf]
;AB[cj]
;AB[di]
;AB[ej]
;AB[dk]
;AB[ji]
;AB[kj]
;AB[jk]
;AB[oj]
;AB[pi]
;AB[qj]
;AB[pk]
;AB[co]
;AB[dn]
;AB[eo]
;AB[dp]
;AB[io]
;AB[jn]
;AB[ko]
;AB[jp]
;AB[mo]
;AB[nn]
;AB[oo]
;AB[np]
;AB[qp]
;AB[pq]
;AB[qr]
;AB[rq]
;AB[id]
;AB[kd]
;AB[if]C[This eye at k15 has 4 sides and 3 diagonals.  Also a true eye.]
;AB[od]
;AB[of]
;AW[qd]
;AW[qc]
;AW[qf]
;AW[rf]C[At q15, black has 4 sides but controls just two of the diagonals.  Two is less than a majority, so Q15 is a false eye.]
;AW[ei]
;AW[ck]
;AW[bk]
;AW[fi]
;AB[ci]
;AB[ek]C[d10 is another false eye because W controls two of the diagonals]
(;AB[ki]
;AB[ii]
;AB[hk]TR[ii]TR[ki]TR[ik]C[k10 is a true eye now, because B controls three diagonals, marked by triangles.

The diagonal at j9 could be taken away if B is not mindful

-- chat --
Nichtogo: 2. From move 0: J10 D16 D15 D14 E14 F14 F15 F16 E16 J15 K14 L15 K16 P15 Q16 R15 Q14 C10 D11 E10 D9 K11 L10 K9 P10 Q11 R10 Q9 C5 D6 E5 D4 J5 K6 L5 K4 N5 O6 P5 O4 R4 Q3 R2 S3 J16 L16 J14 P16 P14 R16 R17 R14 S14 E11 C9 B9 F11 C11 E9 L11 J11 H9 
]
;AW[il]C[If B needs K10 to be a true eye, he must defend at J9 now.  Or mount some other kind of defense (read on).

-- chat --
joncrott: 5. From move 0: J10 D16 D15 D14 E14 F14 F15 F16 E16 J15 K14 L15 K16 P15 Q16 R15 Q14 C10 D11 E10 D9 K11 L10 K9 P10 Q11 R10 Q9 C5 D6 E5 D4 J5 K6 L5 K4 N5 O6 P5 O4 R4 Q3 R2 S3 J16 L16 J14 P16 P14 R16 R17 R14 S14 E11 C9 B9 F11 C11 E9 L11 J11 H9 J8 
]
;AB[oi]
;AB[qi]
;AB[nk]
;AW[ok]C[Similarly, B must do something here if Q9 is to remain a true eye.  That could mean capturing p9 directly with p8, or by a sequences of moves.  Or perhaps B is such a good reader that he knows that W is a captive.  That works, too!]
(;B[pl]
;W[ol]
;B[om]
;W[nl]
;B[ml]
;W[nm]
;B[mm]C[here black had other stones on the board that enabled him to ladder the p9 stone]
)(;AW[ol]
;B[pl]
;W[nl]
;B[ml]
;W[mk]
;B[nj]
;W[ll]
;B[mm]C[If my reading is correct, the white stone at p9 has been doomed all along and I could have tenuki'd (played away) when W placed a stone at p9.  Read carefully!]
))(;B[lg]
;W[nk]
;B[qn]
;W[rm]
;B[ri]
;W[ph]
;B[nh]
;W[mg]
;B[mf]
;W[le]
;B[ld]
;W[gc]
;B[fc]
;W[ec]
;B[dc]
;W[cc]
;B[bd]
;W[cg]
;B[dg]
;W[fg]
;B[gg]
;W[hh]
;B[hj]
;W[hk]
;B[hl]
;W[hm]
;B[hn]
;W[ho]
;B[gp]
;W[gq]
;B[gr]
;W[es]
;B[ds]
;W[br]
;B[ar]
;W[ap]
;B[an]
;W[bl]
;B[el]
;W[em]
;B[fn]
;W[fp]
;B[eq]
;W[er]
;B[dq]
;W[cq]
;B[bp]
;W[bo]
;B[bn]
;W[cm]
;B[dl]
;W[fo]
;B[go]
;W[is]
;B[gs]
;W[iq]
;B[jq]
;W[ks]
;B[kr]
;W[kp]
;B[nr]
;W[or]
;B[mr]
;W[lq]
;B[mp]
;W[oq]
;B[pp]
;W[po]
;B[on]
;W[lm]
;B[kn]
;W[jl]
;B[kl]
;W[ll]
;B[jm]
;W[im]
;B[ik]
;W[lj]
;B[mk]
;W[nm]
;B[om]
;W[pl]
;B[ql]
;W[rn]
;B[ro]
;W[sp]
;B[so]
;W[sl]
;B[rk]
;W[si]
;B[rh]
;W[qh]
;B[sg]
;W[sf]
;B[rd]
;W[rb]
;B[pb]
;W[oc]
;B[nc]
;W[mc]
;B[kb]
;W[lc]
;B[nd]
;W[me]
;B[nf]
;W[og]
;B[oi]
;W[nj]
;B[mi]
;W[li]
;B[kg]
;W[jg]
;B[jh]
;W[gf]
;B[ge]
;W[hd]
;B[hc]
;W[eb]
;B[db]
;W[cb]
;B[ab]
;W[be]
;B[bg]
;W[bh]
;B[ai]
;W[ah]C[

-- chat --
jtfq7695: like i care
]
))(;AB[jr]C[Side of the board, one point eye.

"ALL of the sides" means three sides.  Majority of the diagonals means both diagonals.]
;AB[ir]
;AB[kr]
;AB[ks]
;AB[is]TR[ir]SQ[jr]TR[kr]SQ[is]SQ[ks]C[Squares mark the sides, and triangles mark the diagonals of the true eye at K1]
;AB[os]
;AB[pr]
;AB[qs]
;AB[or]TR[qq]TR[qr]C[q1 is not a true eye yet.  B can make it a true eye by playing either of the triangle points]
;AB[sn]
;AB[rm]
;AB[sl]
;AB[rn]
;AW[rl]
;AW[rk]TR[rl]C[t7 is not a true eye because B does not control one of the diagonals (triangle)]
;AB[qm]
;AB[ql]
;AB[qk]
;AB[qj]
;AB[rj]
;AB[sj]CR[qj]CR[rj]CR[qk]CR[ql]CR[qm]CR[rm]CR[rn]CR[sn]C[Here t7 is a true eye, because B absolutely controls s8.  Even though there is a W stone there, W does not control that intersection because her two stones are dead.  She cannot play t9 (suicide), and she cannot capture the surrounding group (circle stones).  On the other hand, B could play t9 at any time and capture the two W stones.  He will not do so, because that would be playing in his territory and cost him a point.]
;AB[sg]
;AB[rg]
;AB[rf]
;AB[se]
;AB[qe]C[Now T14 is a true eye because B controls both S13 and S15.]
;AW[qc]
;AW[rc]
;AW[rd]C[It is black's turn.  in order to maintain the "true eye" status of t14, he must defend at s15.]
;AB[re]
;AB[na]
;AB[nb]
;AB[mb]
;AB[la]
;AB[lc]
;AW[jb]
;AW[ib]
;AW[lb]C[Again, B must take action to maintain the "true eye" status of N19.]
;AB[kb]
;AE[lb]SQ[la]SQ[na]TR[lb]SQ[mb]TR[nb]C[Now N19 is a true eye.  B controls both diagonals (triangle) and all of the sides (square)]
;AW[gh]C[Now N19 is a true eye.  B controls both diagonals (triangle) and all of the sides (square)]
;AE[gh]
;AW[ao]C[Is M18 a true eye now?]
;AE[ao]TR[ka]TR[ma]SQ[kc]SQ[mc]C[M18 is not a true eye yet.  B controls the triangle points, but needs to control one of the square points before M18 will be a true eye.

This is easily accomplished, because the square points are miai.  If W takes one of them, B can take the other.]
;AW[ja]C[B must react to a move at K19 or L19 in order to keep control of the L19 diagonal.

If W plays a diagonal first, W can claim 2 of the three unclaimed diagonals.

(L19 was controlled by B before.  With K19 at the vital point of the tiger mouth, things have changed!)

]
;AB[ar]
;AB[ao]
;AB[bp]
;AB[al]
;AB[bk]
;AB[cl]TR[bl]TR[ap]TR[as]C[Note that the triangle points are all in the jaw of a tiger mouth.]
;AB[fa]
;AB[eb]
;AB[da]C[Can B make a true eye out of E19?]
;AW[jj]
;AE[jj]
;AB[ac]
;AB[bd]
;AB[ae]
;B[bc]
;W[be]C[With alternating play (not ko, that is), B cannot immediately secure both vital points of E19 or A16.]
;AB[bg]
;B[ce]
;W[bf]
;B[cf]
;W[af]
;B[ag]TR[ac]TR[bc]TR[bd]TR[ae]TR[ce]TR[cf]TR[ag]TR[bg]C[then again, maybe B can capture the offending white stone to get control of the B15 diagonal.

Is this a triangle group a  living group?  Can B safely play somewhere else?

-- chat --
Overcast: "Is this a triangle group a  living group?  Can B safely play somewhere else?" ---> What is a triangle group and a living group? I think B would have to put stones at c16 and c13 before it was safe?
]
;AW[ab]
;AW[bb]
;AW[cc]
;AW[cd]
;AW[de]
;AW[df]
;AW[dg]
;AW[cb]
;AW[cg]
;AW[bh]
;AW[ah]C[How about now?  Is B safe, or does he need another move to make sure his group lives?

-- chat --
ledante: B14 ensures life
]
)(;AB[rr]C[Corners, one point eye

In the corner "all of the sides" means two sides (square).  "majority of the diagonals" 
means the single diagonal (triangle)]
;AB[sr]
;AB[rs]TR[rr]SQ[sr]SQ[rs]C[One true eye.

In the corner "all of the sides" means two sides (squarea).  "majority of the diagonals" 
means the single diagonal (triangle)]
;AB[sb]
;AB[ra]
;AB[qb]TR[rb]TR[rc]C[T19 is a true eye here.  A W stone at either triangle point would require defense by B.]
;AW[rb]
;B[rc]C[eye defended!

now is s18 a true eye?

-- chat --
Hans-Peter-Ingo: 4. From move 0: S2 T2 S1 T18 S19 R18 S18 S17 
]
;AW[jj]TR[qa]TR[sa]TR[sc]C[S18 is a true eye because B controls all 4 sides plus the diagonals (triangles).  As usual, the diagonals at R19 and T17 may require some defense]
;AB[ab]
;AB[ba]
;AB[cb]
;AB[bc]
;W[ad]TR[ac]TR[cc]C[B can keep control of three diagonals by playing at either triangle point]
;B[cc]
;W[da]C[Does B need to reply to D19 to maintain B18 as a true eye?]
;B[kj]
;W[lj]TR[ca]TR[ac]C[Yes, B need to play either C17 or A17 in order to keep this group alive.  If he doesn't, he'll have to make or connect to another eye somewhere.]
)(;AB[fd]C[The turtleback shape has potential to become a one or two point eye]
;AB[ee]
;AB[ef]
;AB[fg]
;AB[gf]
;AB[ge]
;AB[nd]
;AB[oe]
;AB[of]
;AB[ng]
;AB[mf]
;AB[me]
;AB[fl]
;AB[em]
;AB[en]
;AB[fo]
;AB[gn]
;AB[gm]
;AB[nl]
;AB[mm]
;AB[mn]
;AB[no]
;AB[on]
;AB[om]
;AW[dd]
;AW[ed]
;AW[gg]
;AW[hg]
;AW[ld]
;AW[md]
;AW[og]
;AW[pg]
;AW[dl]
;AW[el]
;AW[gl]
;AW[hl]
;AW[ll]
;AE[ll]
;AW[ll]
;AW[ml]
;AW[ol]
;AW[pl]LB[eb:A]LB[mb:B]TR[gd]TR[od]TR[ff]TR[mg]LB[ej:C]LB[mj:D]LB[ml:1]LB[ol:2]TR[fm]MA[nm]TR[go]C[A, B, C.  Controlling the two triangle locations will secure an eye for B.  If it is white's turn to go first, she can prevent black from making an eye inside the turtle back.

In D, a white stone at X removes the possibility of making o7 an eye, unless one of the white groups 1 or 2 can be captured.  B must follow example C to secure an eye in this configuration.]
;B[gc]
;W[eg]
;B[ff]LB[gc:1]TR[gd]LB[ff:3]LB[eg:2]
;W[jj]
;B[oc]
;W[nf]LB[ff:1]
;B[mg]MA[sa]LB[gc:4]LB[oc:1]LB[ff:6]LB[nf:2]LB[eg:5]LB[mg:3]
;W[kj]
;B[fm]
;W[eo]
;B[go]LB[gc:1]LB[oc:4]LB[ff:3]LB[nf:5]LB[eg:2]LB[mg:6]LB[fm:7]LB[eo:8]LB[go:9]
(;W[nm]
;B[nn]C[Blac must look for eyes elsewhere.  O7 is a false eye.]
)(;W[ij]
))(;AE[ij]
(;AB[ji]
;AB[ki]
;AB[lj]
;AB[kk]
;AB[jk]
;AB[ij]C[what does it take for this group to wind up with a real eye?]
;AW[ii]
;AW[ih]
;B[lk]C[black k10 would make this a real eye]
;W[jj]SQ[hk]SQ[ik]SQ[il]
;B[ik]
(;AW[jh]
;AW[kh]
;AW[li]
;W[kj]
)(;W[pi]C[

-- chat --
zia_ahmad: i don't know how to take these lessons
]
))(;AE[ji]
;AE[ki]
;AE[lj]
;AE[kk]
;AE[jk]
;AE[ij]
)))