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The jail is represented by a four by five rectangle as shown. Starting with the square representing Khun Phaen and the rectangles and squares A, B, C, D, E, F, G, H, I, representing the guards in the positions shown in the diagram, you have to slide the pieces, keeping them all inside the jail at all times, to move Khun Phaen past all the guards into the position at the centre bottom from which he can escape to freedom.
The best way to try this challenge is to make yourself a model in cardboard or wood with a rectangular frame to keep all the pieces within bounds.