Stoyan, Y. G., I. Grebennik, V. Kalashnikov, and O. Lytvynenko. “Enumeration and Generation of Permutations With a Partially Fixed Order of Elements”. International Journal of Combinatorial Optimization Problems and Informatics, Vol. 8, no. 1, Jan. 2018, pp. 19-30, https://ijcopi.org/index.php/ojs/article/view/4.