FLAG 12a: ( 1072)
After Black has played both at left, with , and at right, with , it is mandatory for White to stop Black from creating another ko-shape on the upper edge.
seems to be best to do this job successfully.
FLAG 12b: ( 1077)
Under no circumstances, White should try to play the more restrained move of , instead. She will be taken by surprise after Black got "his" additional ko-shape on the upper edge, and lose the game.