When a match is followed by noise, and thus can not be extended into an alignment of two seeds with cost \(<2\), we can discard it, because the promise that there would be a good alignment (ie, relative cost \(<1/k\)) is not held. As we already saw with pre-pruning and path-pruning, if a match covering 1 seed does not into an alignment of cost \(<2\) covering \(2\) seeds, we might as well discard it. Otherwise, it may be possible to extend a match of the left seed to also cover the right seed for cost \(1\), creating a match covering the two seeds with margin \(1\).