Erdős-Sós for digraphs

Dhruv Mubayi, Jacques Verstraete

Every finite loopless Eulerian digraph with no repeated ordered arc, including digraphs with opposite arcs, contains every orientation of every t-edge tree when it has n vertices and more than (t−1)n arcs. Complete bidirected graph unions show the bound is sharp.

Sources for this record

What was already known

The undirected Erdős–Sós theorem did not cover arbitrary orientations. Earlier Eulerian directed-path bounds were weaker than this sharp threshold.

AI involvement AI-led

Mubayi and Verstraëte proposed the directed extension and prompted Astra, which they credit with every proof. The authors revised and explained the presentation; Riordan and Scott supplied a later independent proof.

Authors supplied the directed extension and prompts; Astra is credited with all mathematical proofs.

Importance Notable

The theorem gives a sharp embedding threshold for every oriented tree in Eulerian digraphs.

Limitations

Mubayi and Verstraëte checked the directed-path case of Astra’s argument, not its full oriented-tree proof. Riordan and Scott later proved the complete conclusion independently by another argument.

Technical verification Partial

The authors explicitly checked only the path special case. Riordan–Scott later gave a separate full human proof, which corroborates the result but does not audit Astra’s general-tree argument.

Independent checking

author check of the short path proof; §1 AI Declaration; §3

Checker
Dhruv Mubayi and Jacques Verstraëte
Scope
Theorem 2.2 restricted to directed paths
Basis
Reported by the linked checker
Evidence source

Human understanding Full

The original authors explain the permutation method, and Riordan–Scott give a simpler full human proof of the oriented-tree conclusion.

Correction and publication history

2026-10-18 · publication

The theorem gives a sharp embedding threshold for every oriented tree in Eulerian digraphs.

Read this published revision