Find a placement of a set of seven points in a plane such that if any subset of three points is chosen then at least one pair of points from the subset are unit distance apart.
Hmm. I was just looking at random problems and I saw this problem on the site two days ago. Except that problem asked for the maximum number of points, and did not specify that 7 was possible. A solution for 7 was eventually found by one of the solvers.
Oh, just found it. It is called "Zimmerman's Family Points
" and was posted in 2005. It is a very good problem, and I encourage people to try and solve it before looking up the previous posts,
Edited on May 20, 2017, 10:08 am