In the making or solving of double acrostics, has it ever occurred to
you to consider the variety and limitation of the pair of initial and
final letters available for cross words? You may have to find a word
beginning with A and ending with B, or A and C, or A and D, and so on.
Some combinations are obviously impossible--such, for example, as those
with Q at the end. But let us assume that a good English word can be
found for every case. Then how many possible pairs of letters are
available?