Boyvalenkov, P., and M. Stoyanova. “SPHERICAL 2-DISTANCE SETS WHICH ARE SPHERICAL 3-DESIGNS”. Ann. Sofia Univ. Fac. Math. And Inf., vol. 95, Dec. 2003, pp. 53-58, https://ftl5.uni-sofia.bg./index.php/fmi/article/view/175.