d4rkm4tter: I made a change so special characters in the tag names are possible. Renamed L+1 Group, Crane's Nest, Carpenter's Square, Weak Carpenter's Square.
guile: Unable to add the "L plus One" tag, maybe because of the "plus" interpreted in html. An admin should check if this tag is used anywhere else successfully and maybe rename it if not(or we can switch to the family tag L group)
d4rkm4tter: Yes, that is also the reason why it is not Carpenter's Square. I renamed this tag. It is a simple fix in the code though, to allow special characters in the names. Maybe fixed tomorrow in general.
Tristram1: I think one of the listed solutions is incorrect.
After 1. B a17? 2. W b18, neither I nor Katago can find a way for B to live. For example, if 3. b19, 4 a18 5. e19, 6. c18 kills. If B doesn't play 3. b19, w can just continue with either b19 or c19, to make a dead shape.
I believe b18 is just the vital point here - 1 b18 is the only way to live.
Yes, that is also the reason why it is not Carpenter's Square. I renamed this tag. It is a simple fix in the code though, to allow special characters in the names. Maybe fixed tomorrow in general.