If we have 10 coins arranged in an equilateral triangle and we want to know the minimum number of coins we can remove so that none of the remaining coins form an equilateral triangle the remaining coins form a Fujimura set. See here for more on this problem.
We have been looking at these sets and some generalizations in Polymath1. In the paper "Density Hales-Jewett and Moser numbers" the problem has come up of finding a citation for the original problem. In Martin Gardners article "“Eccentric Chess and Other Problems” which later appeared in his book Mathematical Circus he cites a a “recent book” of Fujimura. And we are trying to find the cited book. At least one person has checked Fujimura's book The Tokyo Puzzles and did not find it there.
So the question is if anyone knows of the book by Fujimura where the problem was introduced.