Let's have a two stage ko. To be a ko master must one be able to win both stages or could one be a ko measter for one stage, but not the other?
Bill: Yes, it is possible for a player to be komaster for one ko but not another, and that holds for approach kos and multi-stage kos?, as well. With approach kos the temperature (size) of the ko increases with each level and a player could have threats small enough to win the first level, but not the next, while the opponent has large enough threats to win the next level, but would have to waste them on the first level with no chance of winning it. Different stages of multi-stage kos may also have different temperatures, with similar effects. With a multi-stage ko it is not unusual to have one player take one stage and then the opponent fills the next stage, because the first player could win it. It is also possible for the opponent to make a ko threat which the first player ignores, and then the opponent completes the threat when the opponent wins the next stage. The opponent was komaster for the second stage but not for the first, since he had to ignore a threat to take the second stage.