HOẠT ĐỘNG TRONG TUẦN

Thời gian: 9h30, Thứ 5, ngày 17/12/2020.

Địa điểm: Phòng 612, nhà A6, Viện Toán học.

Tóm tắt: M.A. Henning and A. Yeo conjectured in [{it SIAM J. Discrete Math.}, 26 (2012), 687 -- 694] that a bipartite digraph of minimum out-degree at least 3 contains two vertex disjoint directed cycles of different lengths. In this paper, we disprove this conjecture. Further, we classify strong tournaments and strong bipartite tournaments of minimum out-degree 3 without two vertex disjoint directed cycles of different lengths.