A Characterization of Mixed Branching Greedoids

Branching greedoids have been dened and characterized for both directed and undirected rooted graphs. Such greedoids can be extended to rooted mixed graphs graphs with both directed and undirected edges. These greedoids are characterized by a list of forbidden minors. If Ω is a rooted mixed graph, its mixed branching greedoid has the edges of Ω as its ground set and the collection of arborescences as its feasible sets. The set of mixed branching greedoids is exactly the set of local forest greedoids withou