HOẠT ĐỘNG TRONG TUẦN

Thời gian: 9h30 Thứ 5, 5/2/2015

Địa điểm: Phòng 201, Nhà A5, Viện Toán học, 18 Hoàng Quốc Việt, Cầu Giấy Hà Nội

Tóm tắt: In connection with colorings of hypergraphs, Henning and Yeo have posed a problem of investigating finite simple digraphs with two vertex disjoint directed cycles of different lengths. In this report, we will classify 3-regular digraphs with girth 2 and no two vertex disjoint directed cycles of different lengths. In particular, we will disprove a conjecture of Henning and Yeo which states that a 3-regular digraph of sufficiently large order contains two vertex disjoint directed cycles of different lengths.