A B C
================== ================== ==================
| +--+ +--+ +--+ | | +--+ +--+ +--+ | | +--+ +--+ +--+ |
| | | | | | | | | | | | | | | | | | | | | | | |
| +--+ +--+ +--+ | | +--+ +--+ +--+ | | +--+ +--+ +--+ |
| | | | | |
| +--+ +--+ +--+ | | +--+ +--+ +--+ | | +--+ +--+ +--+ |
| | | | | | | | | | | | | | | | | | | | | | | |
| +--+ +--+ +--+ | | +--+ +--+ +--+ | | +--+ +--+ +--+ |
| | | | | |
================== ================== ==================
| +--+ +--+ +--+ | | +--+ +--+ +--+ | | +--+ +--+ +--+ |
| | | | | | | | | | | | | | | | | | | | | | | |
| +--+ +--+ +--+ | | +--+ +--+ +--+ | | +--+ +--+ +--+ |
------------------ ------------------ ------------------

]

A man had in his office three cupboards, each containing nine lockers,
as shown in the diagram. He told his clerk to place a different
one-figure number on each locker of cupboard A, and to do the same in
the case of B, and of C. As we are here allowed to call nought a digit,
and he was not prohibited from using nought as a number, he clearly had
the option of omitting any one of ten digits from each cupboard.

Now, the employer did not say the lockers were to be numbered in any
numerical order, and he was surprised to find, when the work was done,
that the figures had apparently been mixed up indiscriminately. Calling
upon his clerk for an explanation, the eccentric lad stated that the
notion had occurred to him so to arrange the figures that in each case