Cho Hye Yeon, recently promoted to 9P in South Korea, wrote 2 books tsumego books.
In particular, the Vol 1 is the one I've been thru and It's impressive the quantity of diagrams! most of the wrong attempts to live/kill are covered. Easily each problem has as 6-8 diagrams and some have even 10 pages of explanations. The explanations remind a lot the recomended way of analysis showed in the book "Tesuji" .. but in highly deeper level. Hye Yeon is really an exceptional teacher.
More than the half of problems are for 1 to 3 dan amateur. Anyway they have little details that make the reading a bit trickiy.. but you learn a lot. After that, the higher problems are really harder (for me)!
I think is one very good piece of work. I must say this volume is useful to practice and understand the reading process.
BTW, all the problems are created by she! She says in her blog that creating this problems is something she loves and it's like drawing.