Time: 9h30, Thursday,  February 5, 2015

 Location: Room 201, Building A5, Institute of Mathematics, 18 Hoang Quoc Viet, Cau Giay, Ha Noi

Abstract: 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.