Given two triangular grids as shown below. On each grid, what is the minimum number of vertices that should be marked so that each triangular cell has at least two marked vertices?
For the first diagram, one can try to either pr
There is a possible $17$ points method,but I don't know how to prove yet. Ove that at least $17$ points must be marked, or come up with a construction for which only $16$ points are needed.