We review previous solutions of problem nr. 10769 posed by Christian Blatter A 1988 paper by C. D. Godsil and J. Zaks [1] states the following result, which is the solution of problem nr. 10769: “Let G be the graph with the points of the unit sphere in three dimensions as its vertices, and two vertices adjacent if and only if they are orthogonal as unit vectors (i.e., their spherical distance i...