Ten-Yen:  the three-layer problem

Here are all the distinct shapes that Ten-Yen's pieces can form with three congruent colors. All these solutions were found by hand. Solvers include Michael Keller of Maryland (who also conceived this challenge), Bjarne Viken of Norway, and Kate Jones.

That these 17 are the complete collection was verified by computer by Prof. Andrejs Cibulis and his doctoral student, Juris Cernenoks, at the University of Latvia in 2013. The challenge of finding additional shapes or proving that there are no others had been open to the world for 10 years. We were happy to design this special award for the Latvian solvers. Congratulations, Andris and Juris!

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