Moving a king in a three-step triangle to lose a turn and shift the move to the opponent.
Why it matters
Sometimes the position is winning if the opponent has to move and drawn if you do. Triangulation is how you hand the move over: the king walks a three-square triangle and arrives back where it started, having used a move the opponent could not.
It only works when one king has spare squares and the other does not. That asymmetry is the thing to look for, and it is what turns a position that seems to repeat into a win.
See it on a board
White would like this position with Black to move. Three king moves later it is the same position, and now it is Black's turn.
Checked: the position really has the feature described.
How to play it
- Confirm the position is a mutual zugzwang: winning with them to move, drawn with you to move.
- Find three squares your king can walk round that keep everything else in place.
- Check that the opponent's king cannot do the same. If it can, the triangle achieves nothing.
At each level
The same idea, said the way it is taught at each age.
Rook · ages 6–9
If a position wins only when the opponent has to move, walk your king in a triangle. You come back to the same square having spent one more move than they can.
Queen · ages 8–11
Triangulation needs squares that do not let the defender improve. Check every square on the triangle for what it gives the opponent time to do.
What goes wrong
- Triangulating into a position that was never mutual zugzwang, so nothing changes.
- Walking the triangle through a square that lets the enemy king make progress.
Questions people ask
- Can the defender triangulate too?
- Sometimes, and that is exactly what you have to check before starting. If both kings have spare squares, the manoeuvre proves nothing.