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- A - the pair of primers closest to the amplified fragment, corresponding to the entire set of parameters.
- B1 - the pair of primers closest to the amplified fragment, corresponding to the entire set of parameters, if B2 and/or B3 exist. Could be the same as A, but not always.
- B2 - the pair of primers corresponding to the entire set of parameters, which has a 4-nucleotide intersection with B1.
- B3 - the pair of primers corresponding to the entire set of parameters, which starts immediately when B1 ends.