Knight Swap: Guarini's knights puzzle
White and black knights trade places on a small board. It is the puzzle published by Paolo Guarini in 1512, and it still takes most people a while to solve.
How it works
- Move one knight at a time with ordinary knight moves, onto empty squares only.
- Get both white knights to the squares where the black knights began, and the other way round.
- The classic 3×3 version has a 16-move answer. Bigger boards follow.
- Stuck? Show solution plays the stored answer, and the run does not count.
What it trains
It is a pure test of seeing how knights move together in a cramped space. The trick is to notice that the squares form a loop, and you are really rotating the knights around it.
Questions
What is the minimum number of moves?
On the classic 3×3 board the swap takes 16 moves.
Who invented it?
It is generally credited to Paolo Guarini di Forlì in 1512, which makes it one of the oldest recorded chess puzzles.