  A haplotype block, or simply a block, is a chromosomal segment, DNA base
sequence or string that occurs in only a few variants or types in the genomes
of a population of interest, and that has an encapsulated or 'private'
frequency distribution of the string types that is not shared by neighbouring
blocks or regions on the same chromosome. We consider two inverse problems of
genetic interest: from just the frequencies of the symbol types (4 base types,
possible single-base alleles) at each position (point, base/nucleotide) along
the string, infer the location of the left and right boundaries of the block
(block extent), and the number and relative frequencies of the string types
occurring in the block (block structure). The large majority of variable
positions in human and also other (e.g., fungal) genomes appear to be
biallelic, i.e., the position allows only a choice between two possible
symbols. The symbols can then be encoded as 0 (major) and 1 (minor), or as
$\uparrow$ and $\downarrow$ as in Ising models, so the scenario reduces to
problems on Boolean strings/bitstrings and Boolean matrices. The specifying of
major allele frequencies (MAF) as used in genetics fits naturally into this
framework. A simple example from human chromosome 9 is presented.
