rpablo007: Which color is to play seems to really matter, because black can play B13, but white can't; black can play at J13, but white can't; white can play at D13 but black can't. So, the moves change a lot depending on which turn is to play.
jhubert: You are right but it is necessary to add L12 and that is the point to solve.
It doesn't seem like this defensive move is necessary, because of the extra liberty