AnoHito: after the 2-2, 2-1 exchange, the play at 1-3 is listed as correct even though it result in a seki where b can no longer reduce the shape to a dead shape.
the correct move is at the 4-1 point since b can atari at 4-2 and still have 2 liberties. This is not possible afer b plays at the 3-1 point in the incorrect solution.
After making a triangle, adding a stone and making a square also kills.