Hirotaka Ebisui is a Japanese mathematician, known as a person who is fascinated with the plane geometry. In the last few years he produced a number of geometric constructions that hold a mathematical property. Many of Hirotaka’s constructions remind us the pictures that we have seen on sangaku tablets from the Edo period and later. The major difference is that his works are always constructions, while the ones on sangaku tablets were always drawings. It is very difficult to evaluate how many such problems Hirotaka Ebisui created. For the last year I have been collecting all Hirotaka’s PDF files and combining them in one large document about 220 pages, and each page containing 3 to 4 theorems. I have been also recreating many of Hirotaka’s constructions in GSP and sometimes in Geometry Expressions. Each of them turns out to be a true mathematical property. Some of these examples will be presented on this web site.

Hirotaka Ebisui

Original Hirotaka’s Ebisui documents are usually very hard to understand and as a result only very few people are able to get a sense from them and appreciate his works.
One day Prof. Gunter Weiss from Technical University in Dresden, in Germany, wrote to me: “I personally am convinced that Hirotaka is a genius with an incredible instinct for extending and generalizing elementary geometric problems in an interesting and surprising way. He stands in the tradition of the so-called "Japanese Temple Geometry" both, concerning the elementary geometric topics as well as in his behavior not to publish his findings others than showing them to friends with the words "I found a new theorem, please enjoy".
He has never had a "scientific pupil" and his work is not "mathematical mainstream" at all. But it is so fascinating!
All this together makes me a true lover of his work, which expresses Japanese philosophy and tradition AND the beauty of pure simple geometry, which has no other aim then Japanese cherry blossoms.
He cannot be forced to work on a certain problem one proposes to him, but he is like a never stopping fountain, when one listens to him and gets stimulated to work on his findings. He very seldom proves his "theorems" and seems to be quite content, if his graphics-software constantly shows the incidences if zoomed. But he also knows the "geometer's toolbox" for elementary geometry very well (Desargues' and Pappus' and Brianchon' theorems, angle at circumference, power of a point with respect to a circle ...) and sometimes adds a proof, if asked for that.
I believe that his findings really are new and that nobody else dealt with this material before him. So the findings (- I call them findings and not theorems -) are due to him.” (1)

Hirotaka Ebisui (phot. January 2011)