pub type NAIDX = u16;Expand description
Nucleic Acid INdeX: we use u16 (0 to 65k), which is plenty for nucleic acids.
Should you ever want to fold longer sequences, beware that P1KEY needs to
be twice as large (in bits) as NAIDX, since pairs (NAIDX, NAIDX) are
compacted into one P1KEY.