Given a strongly connected digraph D of order n and a subset S of V (D), we prove that if any two nonadjacent vertices of S have degree sum at least 2 n - 1, there is a directed cycle in D that contains all the vertices of S. This result generalizes the theorem of Meyniel on hamiltonicity. © 2006 Elsevier B.V. All rights reserved.
Li, H., Flandrin, E., & Shu, J. (2007). A sufficient condition for cyclability in directed graphs. Discrete Mathematics, 307(11–12), 1291–1297. https://doi.org/10.1016/j.disc.2005.11.066