Before revision:  We consider duplication/loss scenarios and characterize unambiguous false-positive (u-fp) orthology assignments, that is, edges in the Best Match Graphs (BMGs) that cannot correspond to orthologs for any gene tree that explains the BMG. We characterize u-fp edges in terms of subgraphs of the BMG and show that, given a BMG, there is a unique "augmented tree" that explains the BMG and identifies all u-fp edges in terms of overlapping sets of species in certain subtrees.
After revision:  We consider duplication/loss scenarios and characterize unambiguous false-positive (u-fp) orthology assignments, that is, edges in the Best Match Graphs (BMGs) that cannot correspond to orthologs for any gene tree that explains the BMG. Moreover, we provide a polynomial-time algorithm to identify all u-fp edges in terms of overlapping sets of species in certain subtrees.