The above write-up, and the one in
"

How to always win at 3D tic-tac-toe"
are true

only for a

3x3x3 grid.

**Nontrivial** (and

**fun!**)
3D tic-tac-toe

*should* be played on a

4x4x4 grid.
Of course, then the

objective is to get

four
in a row.
It is simple to draw the board on a piece of paper,
but takes
a bit of time to learn to

see the

board in

three dimensions. In

high school I spent

many hours of

lunch periods (and

history) playing this.

Below I sketch the board with one of the more difficult
to see
winning positions. (This wasn't a real game, which would have
gone on longer.)
You should think of the first board
as the top board, and the last as the bottom. See if you
can find the winning four in a row. There is a hint at the
bottom.

-----------------
| X | | | |
-----------------
| | | | |
-----------------
| | | O | |
-----------------
| | | | X |
-----------------
-----------------
| O | | | |
-----------------
| | O | | |
-----------------
| | | X | |
-----------------
| | | | |
-----------------
-----------------
| | | | |
-----------------
| | X | | |
-----------------
| | | | |
-----------------
| | | | |
-----------------
-----------------
| X | | | |
-----------------
| | O | | |
-----------------
| | | | |
-----------------
| | | | |
-----------------

Hint: X has won.