Cohn–de Laat–Leijenhorst conjecture on maximal spherical codes from triangle-free strongly regular graphs

Let $G$ be a connected triangle-free strongly regular graph (SRG) other than a complete bipartite graph. Let $e_2$ be the smallest eigenvalue of the adjacency matrix of $G$, and let $C$ be the spherical code obtained by embedding $G$ into the eigenspace corresponding to $e_2$.

Cohn–de Laat–Leijenhorst conjecture. Three-point semidefinite programming bounds prove that $C$ is a maximal spherical code.

This conjecture proposes a broad application of semidefinite programming bounds to embeddings of triangle-free strongly regular graphs. The source attributes the conjecture to Cohn, de Laat, and Leijenhorst; its resolution is not specified here.