         1 2 3 4      n  1 2      m

                (3)   h h h h  ... h ^-H H  ... H
                       1 2 3 4      n   1 2      m

                (4)   -h h h h  ... h ^-H H  ... H
                        1 2 3 4      n   1 2      m

            where

               h   and  H   denote hexadecimal digits
                i        j

               '^'          denotes exponentiation ( base 16 )

            and

               '+' and '-'  have their usual interpretations.

   length   the length o