Sei Shōnagon puzzles online

The Sei Shōnagon pieces

The Sei Shōnagon Chie no Ita, "the wisdom plates of Sei Shōnagon", was first printed in Japan in 1742. It cuts the same square as the tangram into a different seven: no large triangles, but two trapezia, two medium triangles, a small one, a square and a rhomboid. The rhomboid and one of the trapezia change when they are flipped.

How to play

Not sure where to start? How to play has the rules and the controls, and walks through a whole figure one piece at a time. If you would rather learn with the pieces in your hands, the interactive tutorial solves the square with you.

How difficulty is rated

There are four difficulties, each with the tag it wears on the shelf and over the board:

• Difficulty: easyThe outline gives most of the pieces away.
• Difficulty: mediumSome of the pieces have to be worked out.
• Difficulty: hardThe outline gives almost nothing away.
• Difficulty: impossibleOnly the variations, with pieces of their own and one plain shape to fill.

Every tangram puzzle is rated easy, medium or hard, and the rating is measured from the shape rather than guessed. What makes a tangram hard is how little its outline gives away: a piece with its edges on the outside of the figure shows where it goes, while a piece hemmed in by other pieces has to be worked out.

To rate a puzzle, we add up the length of piece edge hidden inside the figure, where one piece meets another and the silhouette shows nothing. The more of it there is, the harder the puzzle. That is why a figure with parts sticking out is usually easy, and a plain square, which looks the simplest of all, is among the hardest. We checked the measure against how long people take over their first solve of each puzzle, and it holds.