1. [1] Aĭzenshtat, A. Ya. The defining relations of the endomorphism semigroup of a finite linearly ordered set, Sib. Mat. Zh., Volume 3 (1962), pp. 161-169
2. [2] Bang-Jensen, Jørgen; Gutin, Gregory Z. Digraphs, Springer London, Springer Monographs in Mathematics (2009)
3. [3] Bankevich, A. V.; Karpov, Dmitriy V. Bounds of the number of leaves of spanning trees, Journal of Mathematical Sciences, Volume 184 (2012) no. 5, pp. 564-572
4. [4] Bondy, Adrian Graph Theory, Springer, Graduate Texts in Mathematics (2008)
5. [5] Cameron, P. J.; Castillo-Ramirez, A.; Gadouleau, M.; Mitchell, J. D. Lengths of words in transformation semigroups generated by digraphs, Journal of Algebraic Combinatorics, Volume 45 (2017) no. 1, pp. 149-170