Dooz (tic-tac-toe): why perfect play always ends in a draw

The key ideas

1. Win if you can

   Complete your own line of three.

2. Block

   If your opponent has two in a line, take the third square.

3. Fork

   Create two lines of two at once — your opponent can only block one.

4. Take the centre

   The centre belongs to four lines; corners to three; edges to two.

Why it's a draw

A computer can look at every possible game. Doing so shows that neither player can force a win if the other always blocks correctly. That is how the “unbeatable” computer in ZIBADISPLAY Dooz works: it checks every possible continuation and never loses.

Beating the easy computer

Start in a corner; if the computer doesn't take the centre, you can often build a fork.

Play on ZIBADISPLAY Dooz.