Stage: 3 Challenge Level: 
The following steps demonstrate how to free Khun Phaen. The
diagrams do not give every step, but they should make it clear how
to move from start to finish.
Working systematically. smartphone. Translations. Cubes. Visualising. Games. Interactivities. Generalising. Mathematical reasoning & proof. Squares.
Published July 2001,September 2004.
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