hexagon7: I don't get it, black just captures with Q18 (upper right orientation). Is it that white creates ko threats with the solution move?
caranthir: White gains a move. Without C18 and playing elsewhere, Black could capture with A19. With the C18D19 exchange, White can play elsewhere and the corner stones are still safe.
White gains a move. Without C18 and playing elsewhere, Black could capture with A19. With the C18 D19 exchange, White can play elsewhere and the corner stones are still safe.