Gentchev, T., and E. Gentcheva. “Factorizations of the Groups $PSp_{6}(q)$”. Ann. Sofia Univ. Fac. Math. And Inf., vol. 86, no. 1, Dec. 1994, pp. 73-78, https://stipendii.uni-sofia.bg/index.php/fmi/article/view/439.