# Edmonds' Branching Theorem in Digraphs without Forward-infinite Paths

## TL;DR

This paper extends Edmonds' branching theorem to a class of infinite digraphs that lack forward-infinite paths, broadening the theorem's applicability beyond previously known cases.

## Contribution

The paper proves that Edmonds' branching theorem holds for infinite digraphs without forward-infinite paths, filling a gap in the understanding of the theorem's scope.

## Key findings

- The theorem applies to a new class of infinite digraphs.
- It confirms the theorem's validity in the absence of forward-infinite paths.
- The result generalizes previous work limited to digraphs without backward-infinite paths.

## Abstract

Let $ D $ be a finite digraph, and let $ V_0,\dots,V_{k-1} $ be nonempty subsets of $ V(D) $. The (strong form of) Edmonds' branching theorem states thatthere are pairwise edge-disjoint spanning branchings $ \mathcal{B}_0,\dots, \mathcal{B}_{k-1} $ in $ D $ such that the root set of $ \mathcal{B}_i $ is $ V_i\ (i=0,\dots,k-1) $ if and only if for all $ \varnothing \neq X\subseteq V(D) $ the number of ingoing edges of $ X $ is greater than or equal to the number of sets $ V_i $ disjoint from $ X $. As was shown by R. Aharoni and C. Thomassen in \cite{aharoni1989infinite}, this theorem does not remain true for infinite digraphs. Thomassen also proved that for the class of digraphs without backward-infinite paths, the above theorem of Edmonds remains true. Our main result is that for digraphs without forward-infinite paths, Edmonds' branching theorem remains true as well.