This is another exercise in re-arranging formulae involving modulus
arithmetic and it illustrates another type of coding system.
Alternatively the pairs (\alpha, \beta) can also be treated as
vectors and matrix algebra used to encode and decode the messages.
Another alternative is to use an encryption formula based on the
numbers 0 to 675 which represent the letter pairs.
In turn 4 people throw away three nuts from a pile and hide a
quarter of the remainder finally leaving a multiple of 4 nuts. How
many nuts were at the start?