Bloom filter example. An example of a Bloom filter with three hash functions. The k-mers a and b have been inserted, but c and d have not. The three hash functions are represented with arrows, and the bits corresponding to the hashes for a and b have been set to 1. The Bloom filter indicates correctly that k-mer c has not been inserted since not all of its bits are set to 1. However, k-mer d is an example of a false positive: it has not been inserted, but since its bits were set to 1 by the insertion of a and b, the Bloom filter falsely reports that d has been seen already.