Extremal digraphs avoiding an orientation of C-4

摘要

Let P-2,P-2 be the orientation of C-4 which consists of two 2-paths with the same initial and terminal vertices. In this paper, we determine the maximum size of P-2,P-2-free digraphs of order n as well as the extremal digraphs attaining the maximum size when n >= 13. (C) 2020 Elsevier B.V. All rights reserved.