Towards a strengthening of the second neighborhood conjecture

A longstanding conjecture of Seymour, called Seymour's second neighborhood conjecture, states that every oriented graph $D$ contains a vertex $x$ with $|N^{++}_D(x)|\geq |N^{+}_D(x)|$.

The conjecture was verified in a few special classes of oriented graphs, and it remains open for general oriented graphs.

We propose a stronger version of the conjecture that every oriented graph $D$ contains a vertex $x$ such that there exists a complete matching from $N^+_D(x)$ to $N^{++}_D(x)$.

We prove that this stronger version holds for every oriented graph with minimum out-degree at most $5$, and also for every $5$-anti-transitive oriented graph.

This implies that every oriented planar graph satisfies the stronger version.