Then at the ninth iteration, A 9 was tagged as +1 since the label of A 9 was determined only by labeled points in kNN model: A 9 is closer to any point in {A 0 ∼ A 8 } than to any point in {B 0 ∼ B 8 }, regardless of the intrinsic structure in data: A 9 ∼ A 10 and B 9 ∼ B 10 are closer to points in lower moon than to points in upper moon.
bootstrapping method uses the unlabeled data under a local consistency based strategy.