Thanks to blyx for the idea in http://goproblems.com/prob.php3?id=23287
(;GM[1]FF[3]
RU[Japanese]SZ[7]HA[0]KM[5.5]
PW[White]
PB[Black]
GN[White (W) vs. Black (B)]
DT[2021-05-14]
SY[Cgoban 1.9.14]TM[30:00(5x1:00)];TR[ac][bc][cc][dc][ec][fc][gc]PL[B]
AW[ed][de][df][ef][ff][eg]
AB[ad][bd][cd][dd][ce][af][bf][cf][cg][dg][fg]
C[Black to kill on this 4x7 board
]
(;B[gg];W[fe]C[WRONG
]TR[ac][bc][cc][dc][ec][fc][gc])
(;B[gf];W[ge]TR[ac][bc][cc][dc][ec][fc][gc]
(;B[fd];W[fe]C[WRONG
]TR[ac][bc][cc][dc][ec][fc][gc])
(;B[fe];W[gg]C[WRONG
]TR[ac][bc][cc][dc][ec][fc][gc])
(;B[ee];W[fe]C[WRONG
]TR[ac][bc][cc][dc][ec][fc][gc])
(;B[gd];W[fe]C[WRONG
]TR[ac][bc][cc][dc][ec][fc][gc])
)
(;B[ge];W[fe]
C[WRONG There are various ko options but black has no threats and white takes first.
]
TR[ac][bc][cc][dc][ec][fc][gc])
(;B[ee];W[fe]C[WRONG
]TR[ac][bc][cc][dc][ec][fc][gc])
(;B[gd];W[fe]C[WRONG
]TR[ac][bc][cc][dc][ec][fc][gc])
(;B[fe]
(;W[ee]C[CHOICE
]TR[ac][bc][cc][dc][ec][fc][gc]
(;B[gf];W[gg]TR[ac][bc][cc][dc][ec][fc][gc]
(;B[ge];W[fd]TR[ac][bc][cc][dc][ec][fc][gc];B[fg]
C[RIGHT Ko and white has no threats.
]TR[ac][bc][cc][dc][ec][fc][gc])
(;B[fd];W[ge]C[WRONG
]TR[ac][bc][cc][dc][ec][fc][gc])
(;B[gd];W[ge]C[WRONG Black has no threats
]
TR[bc][ac][cc][dc][ec][fc][gc])
)
(;B[gg];W[gf]C[WRONG
]TR[ac][bc][cc][dc][ec][fc][gc])
(;B[ge];W[gf]C[WRONG
]TR[ac][bc][cc][dc][ec][fc][gc])
(;B[gd];W[gf]C[WRONG
]TR[ac][bc][cc][dc][ec][fc][gc])
(;B[fd];W[gf]C[WRONG
]TR[ac][bc][cc][dc][ec][fc][gc])
)
(;W[fd]C[CHOICE
]TR[ac][bc][cc][dc][ec][fc][gc]
(;B[gf];W[gg]TR[ac][bc][cc][dc][ec][fc][gc];B[ge];W[ee]
TR[ac][bc][cc][dc][ec][fc][gc];B[fg]
C[RIGHT Ko and white has no threats
]TR[ac][bc][cc][dc][ec][fc][gc])
(;B[gg];W[gf]C[WRONG
]TR[ac][bc][cc][dc][ec][fc][gc])
(;B[ge];W[gf]C[WRONG
]TR[ac][bc][cc][dc][ec][fc][gc])
(;B[ee];W[ge]C[WRONG
]TR[ac][bc][cc][dc][ec][fc][gc])
(;B[gd]C[WRONG If black plays here, white takes at G3 and lives
])
)
)
(;B[fd];W[fe]LB[ee:1][ge:2][gg:3][ed:4][gd:6]
C[WRONG This path cannot be played out on the 7x7 board. But this move will result in the sequence 1-6 (black 5 passes as a ko threat) and white lives.
]
TR[ac][bc][cc][dc][ec][fc][gc])
)