Makhnei, O.V., V.M. Pylypiv, and R.A. Zatorskii. “$m$-Submultisets and $m$-Permutations of Multisets Elements”. Carpathian Mathematical Publications 13, no. 1 (June 30, 2021): 240–258. Accessed November 21, 2024. https://journals.pnu.edu.ua/index.php/cmp/article/view/4693.