The Arc-Weighted Version of the Second Neighborhood Conjecture

Abstract: Seymour conjectured that every oriented simple graph contains a vertex whose second neighborhood is at least as large as its first. Seymour's conjecture has been verified in several special cases, most notably for tournaments by Fisher. One extension of the conjecture that has been used by several researchers is to consider vertex-weighted digraphs. In this paper we introduce a version of the conjecture for arc-weighted digraphs. We prove the conjecture in the special case of arc-weighted tournaments, strengthening Fisher's theorem. Our proof does not rely on Fisher's result, and thus can be seen as an alternate proof of said theorem.