Li Changho Jingjiang Weiqi Shoujin / Errata
The book solution is just , , . But after this, if at , then may not be easy for beginners to find, so it should be mentioned in the solution.
is given as answer, but defeats this. After -, black can't play a. If at , then at .
The correct answer is at : see the next diagram.
In the first solution diagram, and should be played in the opposite order, first. (The next two diagrams show why first fails.)
In the book's solution diagram, is a mistake, and should be at a instead. White sacrifices to prevent from connecting out. (According to KataGo, this may actually be the best play for both sides in some full-board positions, but it doesn't achieve the problem's goal of connecting.)
If black does need to connect out, is the way to do it. After and , if at a then at b catches white in a shortage of liberties.
There is no clear-cut right move here. KataGo thinks that any of black a, b or c next could be best: it gives different answers depending on what the rest of the board looks like. Note that black b captures the two white stones on the left due to a shortage of liberties. (Just for interest, this position does come up in a pro game: Takagawa-Fujisawa, 3rd Honinbo preliminary round, GoGoD 1944-09-06b, at move 53. Takagawa chose b.)
The book gives black a as the solution, and black b as a mistake. In fact, black a fails: white can escape by playing either b or c.