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About the picture in our front page

The picture, YOSHINO Issei designed, symbolizes world-wide expance of Origami. It is well-designed, but, so to speak, a fiction. Strictly speaking, we cannot fold Tsuru with the part surrounded by latitude lines and meridians on a globe. We cannot, not because this part is curved. On this issue, we mention a study by KAWASAKI Toshikazu.
"We can fold a bird base (which can be pasted on a globe) with a sphere square S (the figure surrounded by 4 great arcs) if the sums of opposite sides' lengths are equal. We are to have one more sphere square S* outside S. Since S* has the same property of S, we can also fold a bird base with S*."
Backgroud: MAEKAWA Jun