Figure 4From: A sub-cubic time algorithm for computing the quartet distance between two general treesCounting directed claims. A shared butterfly induces two butterflies in each tree, which will give four pairs of claims, however the butterflies will only be identical in two of these pairs, thus a shared butterfly will be counted twice. A different butterfly also induces four pairs of claims, but since we are counting different butterflies all four will be counted. The way we count shared butterflies prevents the two different butterflies induced by the shared (undirected) butterfly from being counted.Back to article page