First, select a board and give an initial value to all variables. Here we start with x=3, y=2 and z=1.

On each turn a player must connect two neighbouring points.

Connections van be made vertically or horizontally.

Once and only once in the game each player may choose not to connect and may instead increase or decrease one of the variables by 10. Players typically hold these special moves till later on in the game.

Moving forward in the game, we see that neither player has yet used their special turn to increase or decrease a variable by 10.

We are reaching a critical point in the game. Whenever a player completes one of the small square - they steal the contents of that square (whether they want to or not.)

In this case, the player on the left definitely wants the lower left box, so will complete that square in the next slide.

It is worth 5 points.

When a square is completed, the player must take another turn. Sometimes they will not want to do this.

In this case the left player will add a connector in to the bottom of the middle square on the next slide.

That is the end of the left players. turn. Let's skip ahead again...

It is Right's turn. On the next slide he will grab the 2x square.

The 2x square is completed...

Its contents are grabbed. Right must take another turn because he has completed a square. He chooses to complete the square around the x.

Now he grabs the contents of that square.

Right again must take another move because he's completed yet another square. This time he prepares to take his special move. He can only do this once throughout the whole game. He's going to choose to increase or decrease one of the variables by 10.

z is now worth minus 9 points!

That is the end of Right's turn. Let's skip ahead a couple of moves...

One last rule - after all the squares are taken you can no longer make your special move. In the present game both Left and Right have already made their special move (you can see that Left has increased the value of y to 12).

Now we'll skip to the end.

All that need to be done now is substitute the values for the variables to see who has won. Here we see that y is the most valuable and z actually gives negative points. Who wins?

Right wins!

After your students have played a few games they should feel free to agree on different rules before the game commences. Instead of the special move being increasing or decreasing by 10 it may be halving and doubling. Instead of the winner having the most points, it may be that the winner has got the fewest points. Let them get creative and agree on the rules before the game starts.

Here are written instructions and a variety of game-boards.