JPortman: It's a bit strange that there's no "Best result" comment next to the assignment in this problem. A move at 2-1 point (T18 or A18) also makes a living group, though it's less profitable. So if only the most profitable solution is considered right in this problem, it would be nice if this will be dir3ctly mentioned. Or else users will choose for a technically correct solution (a move at 2-1), but it will be considered a mistake
caranthir: As in a life and death problem, T18 is "technically correct". But if this were understood as a general problem of shape, then T18 is so bad that it's just wrong (about -3 points according to Katago). The opponent will either fix at R16 or play away; in the first case they have a flawless shape, or by playing away, a free move, with T18 possibly wasted should we still cut at R16 later. Anyway, I'll add a note in the tree ("too slow").
d4rkm4tter: Even book authors can't stay free of duplicates in their books. I found duplicates in several of the printed out collections when scanning. I changed this problem a bit to make it different.
As in a life and death problem, T18 is "technically correct". But if this were understood as a general problem of shape, then T18 is so bad that it's just wrong (about -3 points according to Katago). The opponent will either fix at R16 or play away; in the first case they have a flawless shape, or by playing away, a free move, with T18 possibly wasted should we still cut at R16 later. Anyway, I'll add a note in the tree ("too slow").