Solutions to worst move puzzles
Puzzle 1
Red captures the cells shaded red, leaving room for only a ziggurat (shaded gray) below to connect. Blue has a 3rd row ladder escape on the left with (*). In order for Blue to win, Red should try to intrude neither the ladder escape nor the ziggurat. Red 1 below achieves this, and it's in fact the unique losing move; Blue 2 is the unique winning reply.
Puzzle 2
Red's unique losing move is 1, and Blue's unique winning reply is 2:
Note that Blue captures the shaded region, hence killing Red 1. Here is a likely continuation:
How do we approach this puzzle? You could solve it with lots of trial and error, but here is one attempt at motivating the answer. Some of Blue's strongest threats are at A, B, and C below:
In particular, A forms edge template IV2d and captures the entire corner region (shaded blue); B is a strong move in combination with d1, analogous to the combination of a9 and b10 in 11×11; and C forms edge template IV2h with f4. This makes the entire bottom half of the board unlikely candidates for Red's losing first move, because any red stone in area allows (*) to connect to bottom right even after Blue plays C.
The moves a1—c1 on the first row intrude on Blue's plan to play A, so they are also unlikely. Note that a1 is particularly tempting, because Blue b2 kills a1. However, Red still wins after Blue b2:
The moves e1/f1 also block Blue's plan to play B, so they seem too strong. We're now a bit stumped, so we refer again to Openings on 11 x 11#a9. We realize that not only is Red b10 strong (for Red) in combination with Red a9, but Blue b10 is also strong (for Blue) against Red a9 — in other words, Red a9 is weak against Blue b10! The analogous statement in our puzzle is that Red f3 is weak against Blue e2. So we check if f3 is losing, and indeed, we come to the surprising fact that Red's unique losing move isn't on the top or bottom row.
Puzzle 3
Puzzle 4
Puzzle 5
Red 1 is the unique losing move, and Blue 2 is the unique winning reply:
