An illustration of a rooted alignment A between Tvand. (a) Each subtree of the form () is either pruned by the alignment, or matched to exactly one subtree of the form (). In this example, is matched to (in red), is matched to (in blue), and is matched to (in green). These three subtree- matchings induce three sub-alignments of A:,, and, respectively, where A is the union of these three sub-alignments (the pair (v,v′) participates in all three sub-alignments). The pruned subtrees in this example are ,, and. (b) The corresponding bipartite matching between N(v) and N(v′).