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 is eventually needed and there is nowhere else to play