It is important to understand the status of the lower right, because the degree to which White's invasion has been successful, is the key of this game.
As explained in the main page, the marked black stones are captured, but they do play a role in the evaluation of the white group in the corner.
White can start a ko here, but Black can capture first. White has a local ko threat at , but the captured marked stones provide plenty of local ko threats too. Moreover, White will have to fight the ko at a as well, so it is a two stage ko for him, while he's behind on threats. This is not a favorable ko to fight at this point in time.