Doubling the cube (∛2)

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1. 

   1. Crease the centre line

   White side up. Fold the left edge to the right edge and unfold to find the middle of the top edge.

2. 

   2. Find a third (Haga’s theorem)

   Fold the bottom-right corner to the middle of the top edge. Where the folded bottom edge crosses the left edge is one third of the way up.

3. 

   3. Mark and unfold

   Pinch a small mark at that point on the left edge, then unfold.

4. 

   4. Lower third crease

   Fold the bottom part up along a horizontal line through the mark, then unfold.

5. 

   5. Upper third crease

   Fold the top edge down to the lower third crease and unfold. The paper is now creased into three equal strips.

6. 

   6. Two points onto two lines (Messer’s fold)

   Fold the bottom-left corner over onto the right edge so that, at the same time, the left end of the lower third crease lands on the upper third crease. The point where the corner touches marks ∛2.