The Hamming distance between two oligonucleotides, in our case, is number of not coinciding positions in these oligonucleotides.

AATGCGT
TAGGCTT
*A**G**T Hamming distance is equal to 5.

If Hamming distance R between oligonucleotides from different sequences is lower than the
threshold value ro, they are united into one class.

We recommend to use ro >( l/2 ).